Magnetic memory including memory cells incorporating data recording layer with perpendicular magnetic anisotropy film

ABSTRACT

A magnetic memory includes a magnetic memory, including a ferromagnetic underlayer including a magnetic material, a non-magnetic intermediate layer disposed on the underlayer, a ferromagnetic data recording layer formed on the intermediate layer and having a perpendicular magnetic anisotropy, a reference layer connected to the data recording layer across a non-magnetic layer, and first and second magnetization fixed layers disposed in contact with a bottom face of the underlayer. The data recording layer includes a magnetization free region having a reversible magnetization and opposed to the reference layer, a first magnetization fixed region coupled to a first border of the magnetization free layer and having a magnetization fixed in a first direction, and a second magnetization fixed region coupled to a second border of the magnetization free layer and having a magnetization fixed in a second direction opposite to the first direction.

The present application is a Divisional application of U.S. patentapplication Ser. No. 13/304,083, filed on Nov. 23, 2011, which is basedon and claims priority from Japanese Patent Application No. 2010-264298filed on Nov. 26, 2010, Japanese Patent Application No. 2011-017965filed on Jan. 31, 2011, and Japanese Patent Application No. 2011-237544filed on Oct. 28, 2011, the entire contents of which are incorporatedherein by reference.

BACKGROUND

The present invention relates to a magnetic memory, more particularly,to a magnetic memory using a magnetic film with perpendicular magneticanisotropy (PMA) as a data recording layer in each memory cell.

The magnetic memory or magnetic random access memory (MRAM) is anon-volatile memory which achieves high speed operation and infiniterewriting tolerance. This encourages practical use of MRAMs in specificapplications, and promotes development for expanding the versatility ofthe MRAMs. A magnetic memory uses magnetic films as memory elements andstores data as the magnetization directions of the magnetic films. Inwriting desired data into a magnetic film, the magnetization of themagnetic film is switched into the direction corresponding to the data.Various methods have been proposed for the switching of themagnetization direction, but all of the proposed methods are the same inthat a current (or write current) is used. It is of much importance toreduce the write current in realizing practical use of MRAMs. Theimportance of the reduction in the write current is discussed in, forexample, N. Sakimura et al., “MRAM Cell Technology for Over 500-MHzSoC”, IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. 42, NO. 4, pp. 830-838,2007.

One approach for reducing the write current is to use “current drivendomain wall motion” in data writing. As disclosed in A. Yamaguchi etal., “Real-Space Observation of Current-Driven Domain Wall Motion inSubmicron Magnetic Wires”, PHYSICAL REVIEW LETTERS, VOL. 92, NO. 7,077205, 2004, when a current is flown in the direction through a domainwall, the domain wall is moved in the direction of the conductionelectrons. Therefore, by flowing a write current through a datarecording layer, the domain wall is moved in the direction correspondingto the current direction, to thereby write desired data. An MRAM basedon current driven domain wall motion is disclosed in, for example,Japanese Patent Application Publication No. 2005-191032 A.

Furthermore, a magnetic shift register based on spin injection isdisclosed in U.S. Pat. No. 6,834,005. This magnetic shift registerrecords data by using domain walls formed in a magnetic body. When acurrent is injected through domain walls in a magnetic body which isdivided into a large number of regions (or magnetic domains), the domainwalls are moved by the current. The magnetization direction of eachregion is defined as recorded data. Such magnetic shift register is usedfor, for example, recording a large amount of serial data.

It is known in the art that the write current is further reduced byusing a magnetic film with perpendicular magnetic anisotropy as a datarecording layer in a magnetic memory which achieves data write based oncurrent driven domain wall motion. Such technique is disclosed in, forexample, S. Fukami et al., “Micromagnetic analysis of current drivendomain wall motion in nanostrips with perpendicular magneticanisotropy”, JOURNAL OF APPLIED PHYSICS, VOL. 103, 07E718, (2008).

Furthermore, international publication No. WO2009/001706 A1 discloses amagnetic memory in which a magnetic film with perpendicular magneticanisotropy is used as a data recording layer and data writing isachieved by current driven domain wall motion. FIG. 1 is a section viewschematically showing a magnetoresistance effect element 200 integratedin the disclosed magnetic memory. The magnetoresistance effect element200 includes a data recording layer 110, a spacer layer 120 and areference layer 130. The data recording layer 110 is formed of amagnetic film with perpendicular magnetic anisotropy. The spacer layer120 is formed of a non-magnetic dielectric layer. The reference layer130 is formed of a magnetic layer having a fixed magnetization.

The data recording layer 110 includes a pair of magnetization fixedregions 111 a and 111 b, and a magnetization free region 113. Themagnetization fixed regions 111 a and 111 b are disposed across themagnetization free region 113. The magnetizations of the magnetizationfixed regions 111 a and 111 b are fixed in the opposite directions (orin antiparallel) by magnetization fixed layers 115 a and 115 b,respectively. More specifically, the magnetization direction of themagnetization fixed region 111 a is fixed in the +z direction by themagnetic coupling with the magnetization fixed layer 115 a, and themagnetization direction of the magnetization fixed region 111 b is fixedin the −z direction by the magnetic coupling with the magnetizationfixed layer 115 b. The magnetization direction of the magnetization freeregion 113, on the other hand, is reversible between +z and −zdirections by a write current which flows from one of the magnetizationfixed regions 111 a and 111 b to the other. As a result, a domain wall112 a or 112 b is formed in the data recording layer 110 depending onthe magnetization direction of the magnetization free regions 113. Dataare stored as the magnetization direction of the magnetization freeregion 113. Data may be considered as being stored as the position ofthe domain wall (which is indicated by the numeral 112 a or 112 b).

The reference layer 130, the spacer layer 120 and the magnetization freeregion 113 of the data recording layer 110 form a magnetic tunneljunction (MTJ). The resistance of the MTJ varies depending on themagnetization direction of the magnetization free region 113, that is,the data written into the data recording layer 110. The data are read asthe magnitude of the resistance of the MTJ.

One important issue of a magnetic memory which uses a data recordinglayer with perpendicular magnetic anisotropy is to enhance theperpendicular magnetic anisotropy of the data recording layer. When aCo/Ni film stack (a stack in which thin Co films and Ni films arealternately laminated) is used as the data recording layer, for examplestrong perpendicular magnetic anisotropy can be achieved by forming theCo/Ni film stack so as to exhibit high fcc (111) orientation; however,it is not so easy to form a Co/Ni film stack with sufficiently high fcc(111) orientation.

Japanese Patent Application Publication No. 2006-114162 A discloses aperpendicular magnetic recording medium including an adhesion layer, asoft magnetic underlayer, an intermediate layer and a perpendicularrecording layer, which are laminated in series over a substrate. Thispatent document discloses a technique for improving the magneticcharacteristics and surface smoothness of the soft magnetic underlayerand for further enhancing the adhesiveness with the substrate.Specifically, the adhesion layer is composed of first and secondunderlayers. The first underlayer is formed of alloy of at least twoelements selected from the group consisting of nickel (Ni), aluminum(Al), titanium (Ti), tantalum (Ta), chromium (Cr) and cobalt (Co), andthe second underlayer is formed of metal tantalum or amorphous alloyincluding Ta doped with at least one element selected from the groupconsisting of Ni, Al, Ti, Cr and Zr.

F. J. A. den Broeder et al., “Perpendicular Magnetic Anisotropy andCoercivity of Co/Ni Multilayers”, IEEE TRANSACTIONS ON MAGNETICS, VOL.28, NO. 5, pp. 2760-2765, (1992) discloses that film deposition on aglass substrate without any underlayer results in strong anisotropy inthe in-plane direction, and discusses that an underlayer is necessary toachieve perpendicular magnetic anisotropy. This non-patent documentdiscloses that a gold (Au) film with (111) orientation is a preferredunderlayer. It should be noted here that the underlayer disclosed inthis non-patent document is formed of non-magnetic material and has athickness of 20 nm or more.

Use of a thick non-magnetic layer as an underlayer as disclosed in thisnon-patent document is not preferable for the magnetic memory shown inFIG. 1, in which the magnetizations of the magnetization fixed regionsof the data recording layer are fixed by the magnetization fixed layersformed under the data recording layer. When an underlayer is used in themagnetic memory shown in FIG. 1, for example, the underlayer is insertedbetween the data recording layer 110 and the magnetization fixed layers115 a and 115 b. In this case, the magnetic coupling between the datarecording layer 110 and the magnetization fixed layers 115 a and 115 bmay be broken by the insertion of a thick non-magnetic layer as theunderlayer, resulting in that the magnetizations of the magnetizationfixed regions 111 a and 111 b are loosed. This is unpreferable fornormally operating the magnetic memory.

SUMMARY

Therefore, an objective of the present invention is to provide amagnetic memory including a data recording layer with perpendicularmagnetic anisotropy, wherein the data recording layer has sufficientlystrong perpendicular magnetic anisotropy and the magnetic couplingbetween the data recording layer and a magnetization fixed layerdisposed under the data recording layer is sufficiently enhanced.

In an aspect of the present invention, a magnetic memory includes: amagnetization fixed layer having perpendicular magnetic anisotropy, amagnetization direction of the magnetization fixed layer being fixed; aninterlayer dielectric; an underlayer formed on upper faces of themagnetization fixed layer and the interlayer dielectric; and a datarecording layer formed on an upper face of the underlayer and havingperpendicular magnetic anisotropy. The underlayer includes: a firstmagnetic underlayer; and a non-magnetic underlayer formed on the firstmagnetic underlayer. The first magnetic underlayer is formed with such athickness that the first magnetic underlayer does not exhibit in-planemagnetic anisotropy in a portion of the first magnetic underlayer formedon the interlayer dielectric.

In another aspect of the present invention, a magnetic memory includes:a magnetization fixed layer having perpendicular magnetic anisotropy; aninterlayer dielectric; an underlayer formed on upper faces of themagnetization fixed layer and the interlayer dielectric; and a datarecording layer formed on an upper face of the underlayer and havingperpendicular magnetic anisotropy. The magnetization fixed layer has afixed magnetization direction. The underlayer includes: a first magneticunderlayer; and a non-magnetic underlayer formed on the first magneticunderlayer. The first magnetic underlayer includes NiFe as majorconstitution and includes at least one non-magnetic element selectedfrom the group consisting of Zr, Ta, W, Hf and V. The thickness of thefirst magnetic underlayer is in a range from 0.5 to 3 nm.

In still another aspect of the present invention, a magnetic memoryincludes: a magnetization fixed layer having perpendicular magneticanisotropy, a magnetization direction of the magnetization fixed layerbeing fixed; an interlayer dielectric; an underlayer formed on upperfaces of the magnetization fixed layer and the interlayer dielectric;and a data recording layer formed on an upper face of the underlayer andhaving perpendicular magnetic anisotropy. The underlayer includes: afirst magnetic underlayer; and a non-magnetic underlayer formed on thefirst magnetic underlayer. The first magnetic underlayer includes Co orFe as major constitution and includes at least one non-magnetic elementselected from the group consisting of Zr, Ta, W, Hf and V. The thicknessof the first magnetic underlayer is in a range from 0.5 to 3 nm.

In still another aspect of the present invention, a magnetic memoryincludes: a ferromagnetic underlayer formed of magnetic material; anon-magnetic intermediate layer disposed on the underlayer; aferromagnetic data recording layer formed on the intermediate layer andhaving perpendicular magnetic anisotropy; a reference layer connected tothe across a non-magnetic layer; and first and second magnetizationfixed layers disposed in contact with a bottom face of the underlayer.The data recording layer includes: a magnetization free region having areversible magnetization and opposed to the reference layer; a firstmagnetization fixed region coupled to a first border of themagnetization free layer and having a magnetization fixed in a firstdirection; and a second magnetization fixed region coupled to a secondborder of the magnetization free layer and having a magnetization fixedin a second direction opposite to the first direction. The intermediatelayer is formed of a Ta film having a thickness of 0.1 to 2.0 nm.

The present invention provides a magnetic memory including a datarecording layer with perpendicular magnetic anisotropy, wherein the datarecording layer has sufficiently strong perpendicular magneticanisotropy and the magnetic coupling between the data recording layerand a magnetization fixed layer disposed under the data recording layeris sufficiently enhanced.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, advantages and features of the presentinvention will be more apparent from the following description ofcertain preferred embodiments taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a section view showing an exemplary configuration of aconventional magnetoresistance effect element;

FIG. 2 is a section view schematically showing an exemplaryconfiguration of a magnetoresistance effect element of a firstembodiment of the present invention;

FIG. 3A is a diagram schematically showing the state of themagnetoresistance effect element into which data “0” are written;

FIG. 3B is a diagram schematically showing the state of themagnetoresistance effect element into which data “1” are written;

FIG. 4A is a graph showing the change in the magnitude of themagnetization of a NiFeW film against the film thickness;

FIG. 4B is a graph showing the change in the magnitude of themagnetization of a NiFeZr film against the film thickness;

FIG. 4C is a graph showing the change in the magnitude of themagnetization of a NiFeTa film against the film thickness;

FIG. 5A is a table showing the change in the coupling field exertedacross a Pt film corresponding to a non-magnetic underlayer against thePt film thickness;

FIG. 5B is a table showing the change in the coupling field exertedacross a Pd film corresponding to a non-magnetic underlayer against thePd film thickness;

FIG. 5C is a table showing the change in the coupling field exertedacross an Ir film corresponding to a non-magnetic underlayer against theIr film thickness;

FIG. 6A is a graph showing the magnetization-field curve of a datarecording layer in embodiment example 1 of the first embodiment for acase where a second magnetic underlayer is not provided;

FIG. 6B is a graph showing the magnetization-field curve of a datarecording layer in embodiment example 1 of the first embodiment for acase where one Co film and one Pt film are layered in a second magneticunderlayer;

FIG. 6C is a graph showing the magnetization-field curve of a datarecording layer in embodiment example 1 of the first embodiment for acase where two Co film and two Pt film are layered in a second magneticunderlayer;

FIG. 6D is a graph showing the magnetization-field curve of a datarecording layer in embodiment example 1 of the first embodiment for acase where three Co film and three Pt film are layered in a secondmagnetic underlayer;

FIG. 6E is a graph showing the magnetization-field curve of a Co/Pt filmstack formed on a Pt film corresponding to a non-magnetic underlayer;

FIG. 7 is a graph showing the definition of the saturation field H_(S);

FIG. 8 is a graph showing the change in the saturation field H_(S)against the number of Co and Pt films in the second magnetic underlayerin embodiment example 1 of the first embodiment;

FIG. 9 is a graph showing the relation among the number of the Co and Ptfilms in the second magnetic underlayer, the saturation field H_(S) andthe write current in embodiment example 1 of the first embodiment;

FIG. 10 is a section view showing the structure of comparative example 1of the first embodiment;

FIG. 11A is a graph showing the relation between the thickness ratio ofthe Co and Pt films in the second magnetic underlayer and the saturationfield H_(S) in embodiment example 1 of the first embodiment, where aNiFeW film is used as a first magnetic underlayer and a Pt film is usedas a non-magnetic underlayer;

FIG. 11B is a graph showing the relation between the thickness ratio ofthe Co and Pt films in the second magnetic underlayer and the saturationfield H_(S) in embodiment example 1 of the first embodiment, where aNiFeV film is used as a first magnetic underlayer and a Au film is usedas a non-magnetic underlayer;

FIG. 12 is a section view schematically showing an exemplaryconfiguration of a magnetoresistance effect element of a secondembodiment of the present invention;

FIG. 13A is a graph showing the dependency of the magnetic tunneljunction on material of a first magnetic underlayer;

FIG. 13B is a graph showing the magnetization-field curve whichindicates the coupling state between a data recording layer and themagnetization fixed layer for a case where the first magnetic underlayeris formed of a NiFeZr film;

FIG. 13C is a graph showing the magnetization-field curve whichindicates the coupling state between a data recording layer and themagnetization fixed layer for a case where the first magnetic underlayeris formed of a NiFeZr film;

FIG. 13D is a graph showing the magnetization-field curve whichindicates the coupling state between a data recording layer and themagnetization fixed layer for a case where the first magnetic underlayeris formed of a CoTa film;

FIG. 13E is a graph showing the magnetization-field curve whichindicates the coupling state between a data recording layer and themagnetization fixed layer for a case where the first magnetic underlayeris formed of a CoTa film;

FIG. 14A is a diagram showing the change in the magnetization-fieldcurve against the thickness of the first magnetic underlayer for a casewhere the first magnetic underlayer is formed of a CoTa film;

FIG. 14B is a graph showing the change in the magnetization-field curveagainst the thickness of the first magnetic underlayer for a case wherethe first magnetic underlayer is formed of a CoTa film;

FIG. 15A is a graph showing the magnetization-field curve of the datarecording layer for a case where the second magnetic underlayer is notprovided in the second embodiment;

FIG. 15B is a graph showing the magnetization-field curve of the datarecording layer for a case where the number of Co and Pt films in thesecond magnetic underlayer is one in the second embodiment;

FIG. 15C is a graph showing the magnetization-field curve of the datarecording layer for a case where the number of Co and Pt films in thesecond magnetic underlayer is two in the second embodiment;

FIG. 16 is a graph showing the change in the saturation field H_(S)against the number of Co and Pt films in the second magnetic underlayerin the second embodiment;

FIG. 17 is a graph showing the relation among the number of the Co andPt films in the second magnetic underlayer, the saturation field H_(S)and the write current in the second embodiment;

FIG. 18 is a graph showing the relation between the thickness ratio ofthe Co and Pt films in the second magnetic underlayer and the saturationfield H_(S) in the second embodiment, where a CoTa film is used as afirst magnetic underlayer;

FIGS. 19A and 19B are section views showing an exemplary structure of amagnetoresistance effect element of a third embodiment of the presentinvention;

FIGS. 20A and 20B are section views showing an exemplary structure of amagnetoresistance effect element of comparative example 1;

FIG. 21A is a graph showing an exemplary magnetization curve for a casewhere an external magnetic field is applied to the data recording layerstructured as shown in FIGS. 20A and 20B;

FIG. 21B is a graph showing an exemplary magnetization curve for a casewhere an external magnetic field is applied to the data recording layerstructured as shown in FIGS. 20A and 20B;

FIG. 22A is a graph showing an exemplary magnetization curve for a casewhere an external magnetic field is applied to the data recording layerstructured as shown in FIGS. 20A and 20B after the data recording layeris subjected to thermal annealing;

FIG. 22B is a graph showing an exemplary magnetization curve for a casewhere an external magnetic field is applied to the data recording layerstructured as shown in FIGS. 20A and 20B after the data recording layeris subjected to thermal annealing;

FIGS. 23A and 23B are section views showing the configuration of amagnetoresistance effect element of embodiment example 1;

FIG. 24A is a graph showing an exemplary magnetization curve for a casewhere an external magnetic field is applied to the data recording layerstructured as shown in FIGS. 23A and 23B;

FIG. 24B is a graph showing an exemplary magnetization curve for a casewhere an external magnetic field is applied to the data recording layerstructured as shown in FIGS. 23A and 23B;

FIG. 25 is a graph showing the relation among the thickness of anintermediate layer, the temperature of the thermal annealing and thesaturation field;

FIG. 26 is a graph showing an exemplary magnetization curve for a casewhere an external magnetic field is applied to the data recording layerstructured as shown in FIGS. 23A and 23B;

FIG. 27 is a block diagram showing an exemplary configuration of amagnetic memory in one embodiment of the present invention; and

FIG. 28 is a circuit diagram schematically showing an exemplaryconfiguration of a memory cell in one embodiment of the presentinvention.

DETAILED DESCRIPTION

The invention will be now described herein with reference toillustrative embodiments. Those skilled in the art will recognize thatmany alternative embodiments can be accomplished using the teachings ofthe present invention and that the invention is not limited to theembodiments illustrated for explanatory purposes.

Embodiments of the present invention are described below with referenceto the attached drawings.

First Embodiment

FIG. 2 is a section view schematically showing an exemplaryconfiguration of a magnetoresistance element 100 in a first embodimentof the present invention. The magnetoresistance effect element 100includes a data recording layer 10, a spacer layer 20, a reference layer30, an underlayer 40 and magnetization fixed layers 50 a and 50 b.

The data recording layer 10 is formed of ferromagnetic material withperpendicular magnetic anisotropy. The data recording layer 10 includesa region in which the magnetization direction is reversible and storesdata as the magnetization state thereof. In detail, the data recordinglayer 10 includes a pair of magnetization fixed regions 11 a and 11 band a magnetization free region 13.

The magnetization fixed regions 11 a and 11 b are disposed adjacent tothe magnetization free region 13. The magnetizations of themagnetization fixed regions 11 a and 11 b are fixed in oppositedirections (or in antiparallel). In the example shown in FIG. 2, themagnetization direction of the magnetization fixed region 11 a is fixedin the +z direction and that of the magnetization fixed region 11 b isfixed in the −z direction.

The magnetization of the magnetization free region 13 is reversiblebetween the +z and −z directions. Therefore, a domain wall is formed inthe data recording layer 10 in accordance with the magnetizationdirection of the magnetization free region 13. In detail, as shown inFIG. 3A, a domain wall 12 is formed between the magnetization freeregion 13 and the magnetization fixed region 11 b, when themagnetization direction of the magnetization free region 13 is directedin the +z direction. When the magnetization direction of themagnetization free region 13 is directed in the −z direction, on theother hand, the domain wall 12 is formed between the magnetization freeregion 13 and the magnetization fixed region 11 a. In other words, thedata recording layer 10 incorporates the domain wall 12, and theposition of the domain wall 12 depends on the magnetization direction ofthe magnetization free region 13.

The spacer layer 20 is disposed adjacent to the data recording layer 10.The spacer layer 20 is disposed in contact with at least the upper faceof the magnetization free region 13 of the data recording layer 10. Thespacer layer 20 is formed of non-magnetic dielectric material.

The reference layer 30 is disposed in contact with the upper face of thespacer layer 20. That is, the reference layer 30 is coupled to the datarecording layer 10 (the magnetization free region 13) across the spacerlayer 20. As is the case with the data recording layer 10, the referencelayer 30 is also formed of ferromagnetic material with perpendicularmagnetic anisotropy, and the magnetization direction thereof is fixed inthe +z or −z direction. In the example of FIG. 2, the magnetizationdirection of the reference layer 30 is fixed in the +z direction.

The aforementioned magnetization free region 13 of the data recordinglayer 10, the spacer layer 20 and the reference layer 30 form a magnetictunnel junction (MTJ). That is, the data recording layer 10 (themagnetization free region 13), the space layer 20 and the referencelayer 30 function as a free layer, a barrier layer and a pinned layer inan MTJ, respectively.

The underlayer 40 is disposed on the bottom face of the data recordinglayer 10 (which is opposed to the substrate). The underlayer 40 is usedfor improving the crystalline orientation of the data recording layer 10to achieve strong perpendicular magnetization anisotropy in the datarecording layer 10. The structure and function of the underlayer 40 willbe discussed in detail later.

The magnetization fixed layers 50 a and 50 b are formed ofmagnetically-hard ferromagnetic material with perpendicular magneticanisotropy, and the magnetization directions of the magnetization fixedlayers 50 a and 50 b are fixed in the +z and −z directions,respectively. The magnetization fixed layers 50 a and 50 b are used tofix the magnetizations of the magnetization fixed regions 11 a and 11 bof the data recording layer 10. The magnetization of the magnetizationfixed region 11 a is fixed by the magnetic coupling with themagnetization fixed layer 50 a and the magnetization of themagnetization fixed region 11 b is fixed by the magnetic coupling withthe magnetization fixed layer 50 b. In this embodiment, themagnetization fixed layers 50 a and 50 b are embedded in the groovesformed on an interlayer dielectric 60. In this embodiment, CoPt alloyfilms or Co/Pt film stacks (film stacks in which thin Co films and Ptfilms are alternately laminated) are used as the magnetization fixedlayers 50 a and 50 b. These hard magnetic materials exhibit strongperpendicular magnetic anisotropy.

The interlayer dielectric 60 is a dielectric film for interlayerisolation generally used in a semiconductor integrated circuit. A SiOxfilm, SiN film or a film stack of these films is used as the interlayerdielectric 60.

It should be noted that electrode layers (not shown) are electricallyconnected to the magnetization fixed regions 11 a and 11 b of the datarecording layer 10, respectively. These electrode layers are used tointroduce a write current into the data recording layer 10. In oneembodiment, the electrode layers may be connected to the magnetizationfixed regions 11 a and 11 b of the data recording layer 10 via theafore-mentioned magnetization fixed layers 50 a and 50 b. Also, anotherelectrode layer (not shown) is electrically connected to the referencelayer 30.

In the magnetoresistance effect element 100, two memory states areallowed which correspond to two magnetization states of the datarecording layer 10, that is, two allowed positions of the domain wall inthe data recording layer 10. When the magnetization direction of themagnetization free region 13 of the data recording layer 10 is directedin the +z direction as shown in FIG. 3A, a domain wall 12 is formed onthe border between the magnetization free region 13 and themagnetization fixed region 11 b. In this case, the magnetizationdirections of the magnetization free region 13 and the reference layers30 are parallel to each other. Therefore, the resistance of the MTJ isrelatively decreased. Such magnetization state is correlated to thememory state of, for example, data “0”.

When the magnetization direction of the magnetization free region 13 ofthe data recording layer 10 is directed in the −z direction as shown inFIG. 3B, on the other hand, the domain wall is formed on the borderbetween the magnetization free region 13 and the magnetization fixedregion 11 a. In this case, the magnetization directions of themagnetization free region 13 and the reference layers 30 areantiparallel to each other. Therefore, the resistance of the MTJ isrelatively increased. Such magnetization state is correlated to thememory state of, for example, data “1”.

It should be noted that the correlation between the magnetization stateof the data recording layer 10 and the two memory states are not limitedto that mentioned above. The data recording layer 10 incorporates thedomain wall 12, and the position of the domain wall 12 corresponds tothe magnetization direction of the magnetization free region 13. As aresult, the data recording layer 10 stores data as the position of thedomain wall 12.

In the magnetoresistance effect element 100 of this embodiment, datawriting is achieved by using current driven domain wall motion. In orderto write data “1” into the magnetoresistance effect element 100 when themagnetoresistance effect element 100 previously stores data “0” (wherethe magnetization directions of the magnetization free region 13 and thereference layer 30 are parallel), a write current is flown from themagnetization fixed region 11 a to the magnetization fixed region 11 bvia the magnetization free region 13. In this case, conduction electronsmove from the magnetization fixed region 11 b to the magnetization fixedregion 11 a via the magnetization free region 13. As a result, a spintransfer torque (STT) is exerted on the domain wall 12 which ispositioned at the border between the magnetization fixed region 11 b andthe magnetization free region 13, and the domain wall 12 moves towardthe magnetization fixed region 11 a. In other words, a current drivedomain wall motion occurs. The current density of the write current isdecreased in the magnetization fixed region 11 a, when the write currentpasses through the border between the magnetization fixed region 11 aand the magnetization free region 13. The motion of the domain wall 12is therefore stopped near the border. In this way, the domain wall 12 ismoved near the border between the magnetization fixed region 11 a andthe magnetization free region 13 to achieve data writing of data “1”.

In order to write data “0” into the magnetoresistance effect element 100when the magnetoresistance effect element 100 previously stores data “1”(where the magnetization directions of the magnetization free region 13and the reference layer 30 are antiparallel), on the other hand, a writecurrent is flown from the magnetization fixed region 11 b to themagnetization fixed region 11 a via the magnetization free region 13. Inthis case, conduction electrons move from the magnetization fixed region11 a to the magnetization fixed region 11 b via the magnetization freeregion 13. As a result, a spin transfer torque is exerted on the domainwall 12 which is positioned at the border between the magnetizationfixed region 11 a and the magnetization free region 13, and the domainwall 12 moves toward the magnetization fixed region 11 b. In otherwords, a current drive domain wall motion occurs. The current density ofthe write current is decreased in the magnetization fixed region 11 b,when the write current passes through the border between themagnetization fixed region 11 b and the magnetization free region 13.The motion of the domain wall 12 is therefore stopped near the border.In this way, the domain wall 12 is moved near the border between themagnetization fixed region 11 b and the magnetization free region 13 toachieve data writing of data “0”.

It should be noted that no change occurs in the magnetization state whendata “0” are written in the state in which data “0” are previouslystored, or when data “1” are written in the state in which data “1” arepreviously stored. This means that the magnetoresistance effect element100 is adapted to overwriting.

The data reading is achieved by using the tunneling magnetoresistive(TMR) effect. Specifically, a read current is flown in the data readingthrough the MTJ (composed of the magnetization free region 13 of thedata recording layer 10, the spacer layer 20 and the reference layer30). The direction of the read current may be reversed. The resistanceof the MTJ is relatively decreased when data “0” are stored in themagnetoresistance effect element 100. On the other hand, the resistanceof the MTJ is relatively increased when data “1” are stored in themagnetoresistance effect element 100. Therefore, data can be identifiedby detecting the resistance of the MTJ.

Next, a description is given of a preferred structure of the datarecording layer 10. Desired characteristics of the data recording layer10 include small saturation magnetization and large spin polarizability.As disclosed in A. Thiaville et al., “Domain wall motion byspin-polarized current: a micromagnetic study”, JOURNAL OF APPLIEDPHYSICS, VOL. 95, NO. 11, pp. 7049-7051, 2004, the current driven domainwall motion occurs more easily as the parameter gμ_(B)P/2eM_(s) islarge, where g is the Land& g factor; μ_(B) is the Bohr magneton; P isthe spin polarizability; e is the elementary electric charge; and M_(s)is the saturation magnetization. Since g, μ_(B) and e are physicalconstants, it is effective for reducing the write current to decreasethe saturation magnetization M_(s) of the data recording layer 10 and toincrease the spin polarizability P.

First, alternate film stacks of transition metals, such as Co/Ni, Co/Pt,Co/Pd, CoFe/Ni, CoFe/Pt and CoFe/Pd, are promising as the magnetic filmwith perpendicular magnetic anisotropy used for the data recording layer10 in terms of the saturation magnetization. It is known in the art thatthe saturation magnetizations of these materials are relatively small.More generally, the data recording layer 10 may be structured as a filmstack in which first and second layers are layered. The first layerincludes any of an Fe film, a Co film and a Ni film or an alloy filmformed of a plurality of materials selected from the group consisting ofFe, Co and Ni. The second layer includes any of a Pt film, a Pd film, aAu film, a Ag film, a Ni film and a Cu film, or an alloy film formed ofa plurality of materials selected from the group consisting of Pt, Pd,Au, Ag, Ni and Cu.

Among the above-described film stacks, the Co/Ni film stack especiallyhas a high spin polarizability. Therefore, a Co/Ni film stack isespecially preferable as the data recording layer 10. Actually, theinventors have confirmed by experiments that the use of a Co/Ni filmstack enables domain wall motion with high controllability

An alternate film stack of transition metals (for example, a Co/Ni filmstack) exhibits perpendicular magnetic anisotropy when being structuredin an fcc (111)-oriented crystalline structure, in which the film stackhas an fcc structure and the (111) faces are layered in theperpendicular direction of the substrate. According to G. H. O.Daalderop et al., “Prediction and Confirmation of Perpendicular MagneticAnisotropy in Co/Ni Multilayers”, PHYSICAL REVIEW LETTERS, VOL. 68, NO.5, pp. 682-685, 1992, the perpendicular magnetic anisotropy of theabove-described film stacks originates from interfacial magneticanisotropy at the interfaces therein. In order to provide improvedperpendicular magnetic anisotropy for the data recording layer 10, it istherefore preferable to dispose an “underlayer” which enables growing analternate film stack of transition metals with an improved fcc (111)orientation.

The magnetoresistance effect element 100 of this embodiment incorporatesthe underlayer 40, which enables growing the data recording layer 10with an improved fcc (111) orientation to achieve improved perpendicularmagnetic anisotropy.

In this embodiment, the underlayer 40 includes three layers: a firstmagnetic underlayer 41, a non-magnetic underlayer 42 and a secondmagnetic underlayer 43. The first magnetic underlayer 41 is formed tocover the upper faces of the magnetization fixed layers 50 a and 50 band the upper face of a portion of the interlayer dielectric 60positioned between the magnetization fixed layers 50 a and 50 b. Thenon-magnetic underlayer 42 is formed to cover the upper face of thefirst magnetic underlayer 41 and the second magnetic underlayer 43 isformed to cover the upper face of the non-magnetic underlayer 42.

The magnetic underlayer 41 is formed of material which intrinsicallyexhibits a ferromagnetic property, but with such a reduced thicknessthat the magnetic underlayer 41 does not exhibit ferromagnetism whenformed on an amorphous film such as the interlayer dielectric 60. Inthis embodiment, the magnetic underlayer 41 includes NiFe as the majorconstituent and is doped with at least one non-magnetic element selectedfrom the group consisting of Zr, Ta, W, Hf and V, wherein theconcentration of the non-magnetic element(s) of the magnetic underlayer41 ranges from 10 to 25 atomic % and the thickness of the magneticunderlayer 41 ranges from 0.5 to 3 nm. The non-magnetic underlayer 42 isformed of a non-magnetic film which has an fcc structure and exhibits astrong (111) orientation. In this embodiment, the non-magneticunderlayer 42 is formed of any of Pt, Au, Pd and Ir with a thickness of0.3 to 4.0 nm. The second magnetic underlayer 43 is formed of a magneticfilm stack in which first and second layers are alternately layered atleast once, wherein the first layer consists of Pt or Pd and the secondlayer consists of Fe, Co or Ni.

Such combination of the first magnetic underlayer 41 and thenon-magnetic underlayer 42 causes the data recording layer 10 to exhibitstrong perpendicular magnetic anisotropy, while enhancing the magneticcoupling between the data recording layer 10 and the magnetization fixedlayers 50 a and 50 b. Schematically, the properties of the firstmagnetic underlayer 41 and the non-magnetic underlayer 42 are differentbetween the portion positioned on the interlayer dielectric 60 and theportions positioned on the magnetization fixed layers 50 a and 50 b. Ingeneral, a film formed on an amorphous film exhibits poor orientation.Therefore, the main issue is to form the data recording layer 10 in anfcc (111)-oriented structure to exhibit improved perpendicular magneticanisotropy, for the portions of the first magnetic underlayer 41 and thenon-magnetic underlayer 42 positioned over the interlayer dielectricfilm 60, which is formed of an amorphous film, such as a SiOx film and aSiN film. For the portions positioned over the magnetization fixedlayers 50 a and 50 b, the main issue is to enhance the magnetic couplingbetween the data recording layer 10 and the magnetization fixed layers50 a and 50 b; when the structure of the underlayer 40 is improper (forexample, when a thick non-magnetic film is used as the underlayer 40 asis the case with the above-described conventional art), this undesirablyweakens the magnetic coupling between the magnetic coupling between thedata recording layer 10 and the magnetization fixed layers 50 a and 50b. The combination of the first magnetic underlayer 41 and thenon-magnetic underlayer 42 in this embodiment satisfies these tworequirements at the same time.

Discussed first are the portions of the first magnetic underlayer 41 andthe non-magnetic underlayer 42 positioned over the interlayer dielectricfilm 60. When formed on the interlayer dielectric 60, which is anamorphous film, the first magnetic underlayer 41 is grown as beingamorphous due to a thin film thickness of 0.5 to 3.0 nm, enlarging thesurface energy thereof. The portion of the first magnetic underlayer 41in contact with the interlayer dielectric 60 is formed in a state inwhich there is substantially no magnetization, due to the amorphousgrowth process. The first magnetic underlayer 41 thus structuredpromotes the closest packed orientation (the orientation with theminimum surface energy face) of the crystalline formed thereon.Furthermore, the non-magnetic underlayer 42 formed on the first magneticunderlayer 41 is grown so that the closest packed face thereof isoriented to face the fcc (111) face, since the non-magnetic underlayer42 is formed of any of Pt, Au, Pd and Ir, and a film formed of any ofthese materials intrinsically has the fcc structure. The data recordinglayer 10 can be formed with a strong perpendicular magnetic anisotropyby forming a magnetic film above the non-magnetic underlayer 42, whereinthe magnetic film has an fcc structure and exhibits a strongperpendicular magnetic anisotropy for the (111) orientation. It shouldbe noted that the data recording layer 10 can be formed with a strongperpendicular magnetic anisotropy due to the provision of the firstmagnetic underlayer 41, even when the non-magnetic underlayer 42 has athin film thickness.

The portions of the first magnetic underlayer 41 and the non-magneticunderlayer 42 positioned over the magnetization fixed layers 50 a and 50b, on the other hand, effectively enhances the magnetic coupling betweenthe data recording layer 10 and the magnetization fixed layers 50 a and50 b. For a case where the magnetization fixed layers 50 a and 50 b areformed of hard magnetic material, such as a Co/Pt film stack and a Co—Ptalloy film, as is the case of generally-used magnetization fixed layers,the magnetizations of portions of the first magnetic underlayer 41 aredirected in the perpendicular directions which are the same directionsof that of the magnetization fixed layers 50 a and 50 b, respectively,due to the magnetic interactions from the magnetization fixed layers 50a and 50 b, when the first magnetic underlayer 41 and the non-magneticunderlayer 42 are subsequently layered over the magnetization fixedlayers 50 a and 50 b. Such magnetic interactions fix the magnetizationsof portions of the data recording layer 10 via the non-magneticunderlayer 42, resulting in that the magnetization fixed regions 11 aand 11 b are formed in the data recording layer 10. It should be notedthat a strong magnetic coupling is achieved between the data recordinglayer 10 and the magnetization fixed layers 50 a and 50 b, due to thethin film thickness of the non-magnetic underlayer 42 (0.5 to 4.0 nm).

One may consider that there is a possibility in which the directdeposition of the first magnetic underlayer 41 on the interlayerdielectric 60 may cause an undesired magnetic influence whichdeteriorates the perpendicular magnetic anisotropy. That is, one mayconsider that the formation of the first magnetic underlayer 41 on theamorphous interlayer dielectric 60 may cause the first magneticunderlayer 41 to exhibit in-plane magnetic anisotropy, deteriorating theperpendicular magnetic anisotropy of the data recording layer 10;however, the first magnetic underlayer 41 does not actually cause anundesired magnetic influence which deteriorates the perpendicularmagnetic anisotropy of the data recording layer 10, since the firstmagnetic underlayer 41 is formed so that the first magnetic underlayer41 has substantially no magnetization in the portion disposed on theinterlayer dielectric 60. Therefore, an improved perpendicular magneticanisotropy is also achieved in the data recording layer 10.

The second magnetic underlayer 43 functions as a template of thecrystalline orientation of the data recording layer 10 to improve thefcc (111) orientation of the data recording layer 10, enhancing theperpendicular magnetic anisotropy. In this embodiment, the secondmagnetic underlayer 43 is formed of a film stack in which first andsecond layers are layered at least once, wherein the first layer isformed of Pt or Pd and the second layer is formed of Fe, Co or Ni. Thesecond magnetic underlayer 43 thus structured effectively improves thefcc (111) orientation of the data recording layer 10 formed of a Co/Nifilm stack, enhancing the perpendicular magnetic anisotropy thereof. Inaddition, the second magnetic underlayer 43 thus structured allowsadjustment of the perpendicular magnetic anisotropy of the datarecording layer 10, by adjusting the numbers of the first and secondlayers layered in the second magnetic underlayer 43. It is preferablethat the perpendicular magnetic anisotropy of the data recording layer10 is adjusted into an appropriate range, since the write current may beincreased if the perpendicular magnetic anisotropy of the data recordinglayer 10 is excessively strong.

It should be noted that the second magnetic underlayer 43 may beunnecessary when a magnetic film in which an fcc (111)-orientedstructure is easily formed is used as the data recording layer 10. Whena Co/Ni film stack is used as the data recording layer 10, for example,direct deposition of the data recording layer 10 on the non-magneticunderlayer 42 formed of Pt, Au, Pd or Ir does not result in strongperpendicular magnetic anisotropy. To address this problem, the use ofthe second magnetic underlayer 43 effectively achieves strongperpendicular magnetic anisotropy when a Co/Ni film stack, in which anfcc (111)-oriented structure is not easily formed, is used as the datarecording layer 10. When a magnetic film in which a fcc (111)-orientedstructure is easily formed (for example, a magnetic film stack whichincludes at least one first layer composed of Pt or Pd and at least onesecond layer composed of Fe, Co or Ni), is used as the data recordinglayer 10, on the other hand, the data recording layer 10 may be formeddirectly on the non-magnetic underlayer 42.

As discussed above, the use of the underlayer 40, which is formed as thefilm stack composed of the first magnetic underlayer 41, thenon-magnetic underlayer 42 and the second magnetic underlayer 43, causesthe data recording layer 10 to exhibit strong perpendicular magneticanisotropy while enhancing the magnetic coupling between the datarecording layer 10 and the magnetization fixed layers 50 a and 50 b. Theinventors have confirmed the above-described facts through experiments.The experimental results are described below.

Experiment 1 Magnetic Property of First Magnetic Underlayer 41

First, a description is given of the magnetic property and a preferredthickness range of the first magnetic underlayer 41. In general, theproperty of the first magnetic underlayer 41 is different between theportion in contact with the interlayer dielectric 60 (formed of a SiN orSiOx film) and the portions in contact with the magnetization fixedlayers 50 a and 50 b, as described above.

In order to study the portion of the first magnetic underlayer 41 incontact with the interlayer dielectric 60 (formed of a SiN or SiO₂film), NiFeW films were deposited on substrates each including a SiNfilm or a SiOx film formed on a Si substrate, and the magnetizations ofthe NiFeW films were measured. The thicknesses of the deposited NiFeWfilms were in the range from 1 to 10 nm. The NiFeW films include 12.5atomic % tungsten (W), and the remainder was NiFe base metal. The ratioof Ni to Fe in the NiFe base metal is Ni:Fe=77.5:22.5. All the sampleswere subjected to annealing at 350° C. for two hours in vacuum. Amagnetic field is applied in the perpendicular direction to the filmsurface in the measurement of the magnetization of each sample. For athickness range from 1 to 10 nm, the NiFeW films do not exhibit an M-Hhysteresis loop of a rectangular shape and this confirms such NiFeWfilms are non-ferromagnetic films or in-plane magnetization films.

FIG. 4A is a graph showing the change in the magnitude of themagnetization of the NiFeW film against the film thickness. As shown inFIG. 4A, the magnetization tends to monotonously increase as the filmthickness increases for film thicknesses of 4 nm or more, regardless ofwhich of SiN and SiOx films is disposed just beneath the NiFeW film. Forfilm thicknesses of 0.5 nm to 3 nm, especially less than 2 nm, on theother hand, considerably-reduced magnetizations were observed comparedto those of the NiFeW films of a film thickness of 4 nm or more, in bothcases of the SiN film and the SiOx film. This result indicates that aNiFeW film does not exhibit magnetization with a thin film thickness,when the NiFeW film is deposited on the interlayer dielectric 60.

As thus described, the use of a NiFeW film of a thickness of 0.5 to 3 nmas the first magnetic underlayer 41 eliminates the magnetic influence onthe second magnetic underlayer 43 via the non-magnetic layer 42 andthereby avoids disturbance on the perpendicular magnetic anisotropy ofthe second magnetic underlayer 34, causing no influence on theperpendicular magnetic anisotropy of the data recording layer 10 formedas a Co/Ni film stack. This allows providing improved fcc (111)orientation for the data recording layer 10 formed as a Co/Ni filmstack.

On the contrary, the use of a NiFeW film with a film thickness more than3 nm as the first magnetic underlayer 41 is unpreferable, since the useof such NiFeW film undesirably weakens the perpendicular magneticanisotropy of the data recording layer 10 due to the magnetic influenceon the second magnetic underlayer 43 and the data recording layer 10 viathe non-magnetic underlayer 42.

Furthermore, the use of a NiFeW film with a film thickness less than 0.5nm as the first magnetic underlayer 41 undesirably deteriorates the fcc(111) orientation of the data recording layer 10, since the surfaceunevenness of the interlayer dielectric 60 influences the non-magneticunder layer 42 via the first magnetic underlayer 41. As is understoodfrom the above-described discussion, the preferred thickness range ofthe NiFeW film for the first magnetic underlayer 41 is 0.5 to 3 nm.

The same applies to a case where at least one non-magnetic elementselected from the group consisting of Zr, Ta, Hf and V is doped to NiFebase metal in place of W. For example, FIG. 4B is a graph showing thechange in the magnitude of the magnetization of the NiFeZr film againstthe film thickness, and FIG. 4C is a graph showing the change in themagnitude of the magnetization of the NiFeTa film against the filmthickness. It should be noted that FIGS. 4B and 4C were obtained bydepositing NiFeZr films and NiFeTa films on substrates which incorporatea SiN film formed on a Si substrate and measuring the magnetizations ofthe NiFeZr films and the NiFeTa films. Also for the NiFeZr and NiFeTafilms, considerably reduced magnetizations were observed in a filmthickness range of 0.5 nm to 3 nm, especially less than 2 nm. Thisresult indicates that NiFeZr and NiFeTa films do not exhibitmagnetization with a thin film thickness, when the NiFeW and NiFeTafilms are deposited on the interlayer dielectric 60.

As is understood from the above-described discussion, the first magneticunderlayer 41 preferably has a film thickness from 0.5 nm to 3 nm, morepreferably, less than 2 nm.

Experiment 2 Crystalline Structure of First Magnetic Underlayer 41

Next, a description is given of experimental results concerning therelation between the non-magnetic dopant concentration and thecrystalline structure of the first magnetic underlayer 41, whichincludes NiFe as the major constitute and at least one non-magneticelement selected from the group consisting of Zr, Ta, W, Hf and V.Formed in this experiment were films composed of NiFe base metal dopedwith any of Zr, Ta, W, Hf and V. The crystalline structures of theformed films were analyzed by using an X-ray diffractometer. Thecomposition of the NiFe base metal, which is the major constituent, wasNi:Fe=77.5:22.5. The thickness of the formed films was 15 nm.

The results showed that the NiFeX films (X: Zr, Ta, W, Hf or V), whichwere doped with at least one non-magnetic element selected from thegroup consisting of Zr, Ta, W, Hf and V, exhibited diffraction profileswith broad peaks for non-magnetic dopant concentrations of 10 to 25atomic %; this indicates that the NiFeX films has an amorphousstructure. For non-magnetic dopant concentrations less than 10 atomic %,a crystalline structure resulting from NiFe was observed. Fornon-magnetic dopant concentrations more than 25 atomic %, diffractionpeaks of compounds and mixtures of NiFe and the non-magnetic elementwere observed. This suggests that the preferred concentration of thenon-magnetic element is 10 to 25 atomic %, when a NiFeX film (X: Zr, Ta,W, Hf and V), which is doped with at least one non-magnetic elementselected from the group consisting of Zr, Ta, W, Hf and V, is used asthe first magnetic underlayer 41.

As described above, the first magnetic underlayer 41, which includesNiFe as the major constituent and at least one non-magnetic elementselected from the group consisting of Zr, Ta, W, Hf and V, exhibitssubstantially no magnetization when the film thickness of the firstmagnetic underlayer 41 is adjusted to 0.5 to 3 nm. The dopantconcentration of the non-magnetic element (Zr, Ta, W, Hf or V)preferably ranges from 10 to 25 atomic %.

Experiment 3 Magnetic Coupling between Data Recording Layer 10 andMagnetization Fixed Layers 50 a and 50 b

Next, a description is given of experimental results concerning therelation between the thickness of the non-magnetic underlayer 42 and themagnitude of the magnetic coupling between the data recording layer 10and the magnetization fixed layers 50 a and 50 b. In this experiment,film stacks were formed each of which includes films corresponding tothe magnetization fixed layers 50 a, 50 b, the first magnetic underlayer41, the non-magnetic underlayer 42, the second magnetic underlayer 43and the data recording layer 10. Co/Pt film stacks, in which Co and Ptfilms are alternately layered, were used as the magnetic filmscorresponding to the magnetization fixed layers 50 a and 50 b. NiFeZrfilms of a thickness of 1.5 nm were used as the films corresponding tothe first magnetic underlayer 41, and Pt films were used as the filmscorresponding to the non-magnetic underlayer 42. Co/Pt film stacks inwhich multiple Co films of a thickness of 0.4 nm and multiple Pt filmsof a thickness of 0.8 nm were alternately layered were used as the filmscorresponding to the second magnetic underlayer 43. Finally, Co/Ni filmstacks in which five Co films of a thickness of 0.3 nm and five Ni filmsof a thickness of 0.6 nm were alternately layered were used as the filmscorresponding to the data recording layer 10. Samples of theabove-described structures in which the Pt films corresponding to thenon-magnetic layer 42 have different thicknesses in the range of 0.3 to5 nm were prepared, and the magnetic properties thereof were measured.All of the prepared samples were previously subjected to annealing at350° C. for two hours in vacuum.

FIG. 5A is a table showing the change in the coupling magnetic fieldexerted via the Pt film (which corresponds to the non-magneticunderlayer 42) against the film thickness of the Pt film. As shown inFIG. 5A, coupling magnetic fields of 1900 to 1975 (Oe) were observedacross the Pt film corresponding to the non-magnetic underlayer 42 in afilm thickness range of 0.5 to 4.0 nm. The inventors consider that thisresult arises from the following reason: Since the Co/Pt film stackcorresponding to the magnetization fixed layers 50 a and 50 b functionsas an underlayer of the NiFeZr film corresponding to the first magneticunderlayer 41, the thin NiFeZr film exhibits perpendicular magneticanisotropy due to the influence of the magnetization of the Co/Pt filmstack. Furthermore, the perpendicular magnetizations of the Co/Pt filmstack and the NiFeZr film have an influence on the Co/Pt film stackcorresponding to the second magnetic underlayer 43 via the Pt filmcorresponding to the non-magnetic underlayer 42, resulting in a magneticcoupling for reduced thicknesses of the Pt film. Furthermore, the Co/Ptfilm stack corresponding to the second magnetic underlayer 43 ismagnetically coupled to the Co/Ni film stack corresponding to the datarecording layer 10. As a result, a coupling magnetic field of about 1900to 1975 (Oe) is generated via the Pt film corresponding to thenon-magnetic underlayer 42. This implies that the magnetizations of themagnetization fixed regions 11 a and 11 b of the data recording layer 10can be fixed by the magnetic coupling between the magnetization fixedlayers 50 a, 50 b and the data recording layer 10.

For the film thicknesses of 4.5 nm or more, on the other hand, thecoupling magnetic field exerted via the Pt film corresponding to thenon-magnetic underlayer 42 was zero. This implies that the use of a Ptfilm of a thickness of 4.5 nm or more as the non-magnetic underlayer 42results in that the magnetizations of the magnetization fixed layers 50a and 50 b and the data recording layer 10 are not magnetically coupled,that is, the magnetizations of the magnetization fixed regions 11 a and11 b of the data recording layer 10 are not fixed.

It should be noted that the coupling magnetic field is relatively smallwhen the thickness of the Pt film corresponding to the non-magneticunderlayer 42 is as thin as 0.3 nm, although the Co/Pt film stackcorresponding to the magnetization fixed layers 50 a and 50 b ismagnetically coupled to the Co/Ni film stack corresponding to the datarecording layer 10. This is because the Pt film does not exhibit asufficient fcc (111) orientation, and therefore the Co/Ni film stackdeposited thereon also exhibits a poor fcc (111) orientation. As isunderstood from the above-described discussion, when a Pt film is usedas the non-magnetic underlayer 42, the Pt film preferably has a filmthickness of 0.5 to 4.0 nm.

Similar results were obtained for a case where any of a Au film, a Pdfilm and an Ir film is used instead of the Pt film. For example, FIG. 5Bis a table showing the change in the coupling magnetic field exerted viaa Pd film against the film thickness of the Pd film, when a NiFeTa filmof a thickness of 1.5 nm is used as the film corresponding to the firstmagnetic underlayer 41, and the Pd film is used as the filmcorresponding to the non-magnetic underlayer 42. As shown in FIG. 5B, acoupling magnetic field of 1910 to 1975 (Oe) was observed via the Pdfilm corresponding to the non-magnetic underlayer 42 for filmthicknesses of 0.5 to 4.0 nm. When the film thickness of the Pd filmcorresponding to the non-magnetic underlayer 42 is 4.5 nm or more, thecoupling magnetic field was zero or a value close to zero. Also, whenthe film thickness of the Pd film corresponding to the non-magneticunder layer 42 was as thin as 0.3 nm, a relatively reduced couplingmagnetic field of 1630 (Oe) was observed.

Furthermore, FIG. 5C is a table showing the change in the couplingmagnetic field exerted via an Ir film against the film thickness of theIr film, when a NiFeTa film of a thickness of 1.5 nm is used as the filmcorresponding to the first magnetic underlayer 41, and the Ir film isused as the film corresponding to the non-magnetic underlayer 42. Asshown in FIG. 5C, a coupling magnetic field of 1930 to 1965 (Oe) wasobserved via the Ir film corresponding to the non-magnetic underlayer 42for film thicknesses of 0.5 to 4.0 nm. When the film thickness of the Irfilm corresponding to the non-magnetic underlayer 42 is 4.5 nm or more,the coupling magnetic field was zero. Also, when the film thickness ofthe Ir film corresponding to the non-magnetic under layer 42 was as thinas 0.3 nm, a relatively reduced coupling magnetic field of 1700 (Oe) wasobserved.

The above-described results indicate that the non-magnetic underlayer 42preferably has a thickness of 0.5 to 4.0 nm.

Experiment 4 Magnetic Property of Magnetoresistance Effect Element 100

In the following, a description is given of experimental resultsconcerning the magnetic property of the magnetoresistance effect element100 to which the above-described underlayer 40 is applied. In thisexperiment, magnetoresistance effect elements 100 to which theabove-described underlayer 40 is applied were actually manufactured andmagnetic properties of the data recording layers 10 were measured.

Magnetoresistance effect elements 100 of the following structures wereprepared as embodiment examples 1. A first magnetic underlayer 41, anon-magnetic underlayer 42 and a second magnetic underlayer 43 weresequentially layered in this order as the underlayer 40 of eachmagnetoresistance effect element 100. A NiFeZr film of a thickness of1.5 nm was used as the first magnetic underlayer 41, and a Pt film of athickness of 2 nm was used as the non-magnetic underlayer 42. A magneticfilm stack in which multiple Co films of a thickness of 0.4 nm andmultiple Pt films of a thickness of 0.8 nm were alternately layered wasused as the second magnetic underlayer 43. A Co/Ni film stack in whichfive Co films of a thickness of 0.3 nm and five Ni films of a thicknessof 0.6 nm were alternately layered was used as the data recording layer10. The magnetoresistance effect elements 100 of the above-describedstructure were prepared, wherein the number of the Co and Pt films inthe second magnetic underlayer 43 was varied from zero to four. Thewidth of the magnetoresistance effect elements 100 was 100 nm. Thesemagnetoresistance effect elements 100 were subjected to annealing at350° C. for two hours in vacuum, after the underlayer 40 and the datarecording layer 10 were formed.

FIGS. 6A to 6D are diagrams showing the magnetization-field curves ofthe data recording layers 10 for cases where the number of the Co and Ptfilms within the second magnetic underlayer 43 was zero to three. Forthe case where the number of the Co and Pt films was zero (that is, thecase where the second magnetic underlayer 43 was not provided), as shownin FIG. 6A, the data recording layer 10 exhibited relatively weakperpendicular magnetic anisotropy, incorporating an in-planemagnetization component. As shown in FIGS. 6B to 6D, there was atendency in which the M-H loops became more rectangular and theperpendicular magnetic anisotropy was enhanced as the number of thelayered Co and Pt films was increased. This implies that the use of thesecond magnetic underlayer 43 enables achieving strong perpendicularmagnetic anisotropy for the case where a Co/Ni film stack, for which itis relatively difficult to achieve the fcc (111) orientation, is used asthe data recording layer 10, even after the annealing at 350° C. for twohours.

A similar measurement was done for a case where a NiFeZr film of athickness of 1.5 nm and a Pt film of a thickness of 2 nm were used asthe first magnetic underlayer 41 and the non-magnetic underlayer 42,respectively, and a Co/Pt magnetic film stack in which a Co film of athickness of 0.4 nm and a Pt film of a thickness of 0.8 nm was layeredwas deposited on the non-magnetic underlayer 42. The number of the Cofilm and the Pt film in the Co/Pt magnetic film stack was one. FIG. 6Eis a diagram showing the magnetization-field curve for the case wherethe Co/Pt magnetic film stack was used. As shown in FIG. 6E, amagnetization-field curve with an improved rectangular shape wasobtained for the Co/Pt magnetic film stack, in which fcc (111)orientation is relatively easily formed.

This fact has two technical meanings. First, the use of a Co/Pt magneticfilm stack as the data recording layer 10 effectively achieves strongperpendicular anisotropy for the data recording layer 10. Second, theuse of a Co/Pt magnetic film stack as the second magnetic underlayer 43enables forming the second magnetic underlayer 43 with improved fcc(111) orientation, effectively improving the perpendicular magneticanisotropy of the data recording layer 10 formed thereon (for example,formed of a Co/Ni magnetic film stack).

Furthermore, the saturation field Hs was measured for a case where aCo/Pt magnetic film stack was used as the second magnetic underlayer 43and a Co/Ni magnetic film stack was used as the data recording layer 10.FIG. 7 shows the definition of the saturation field Hs in the presentapplication. In the present application, the saturation field H_(S) isdefined as the magnitude of the external magnetic field at which themagnetizations in the data recording layer 10 are completely directed inthe direction of the external magnetic field when the external magneticfield is applied in the in-plane direction of the data recording layer10. In FIG. 7, for example, H_(S1) indicates the saturation field ofsample (1) and H_(S2) indicates the saturation field of sample (2). Alarge saturation field implies that the perpendicular magneticanisotropy is large. In FIG. 7, for example, the saturation field H_(S)(that is, the magnetic field which completely directs the magnetizationsin the direction thereof) of sample (1) is larger than that of sample(2), and this implies that the perpendicular magnetic anisotropy ofsample (1) is larger than that of sample (2).

FIG. 8 shows the change in the saturation field H_(S) of the datarecording layer 10 against the number of the Co and Pt films in thesecond magnetic underlayer 43, where the number of the Co and Pt filmswas varied from zero to four. As is understood from FIG. 8, thesaturation field H_(S) was increased as the number of the Co and Ptfilms in the second magnetic underlayer 43; this implies that theperpendicular magnetic anisotropy was enhanced as the number of the Coand Pt films was increased.

FIG. 9 shows the changes in the saturation field H_(S) and the writecurrent against the number of the Co and Pt films in the second magneticunderlayer 43. The magnitude of the write current is defined as theminimum write current necessary for causing domain wall motion in thedata recording layer 10. Details of the experimental procedure are alsodescribed in T. Suzuki et al., “Evaluation of Scalability forCurrent-Driven Domain Wall Motion in a Co/Ni Multilayer Strip for MemoryApplications”, IEEE TRANSACTIONS ON MAGNETICS, VOL. 45, NO. 10, pp.3776-3779, (2009), the disclosure of which is incorporated herein byreference.

For samples in which the number of the Co and Pt films in the secondmagnetic underlayer 43 was zero (this implies that the second magneticunderlayer 43 was not deposited), domain wall motion by the current wasnot observed clearly, resulting in an unsuccessful measurement of thewrite current. This can be considered as resulting from that the datarecording layer 10 exhibited relatively weak perpendicular magneticanisotropy and incorporated in-plane magnetization components as shownin FIG. 6A.

For cases where the number of the Co and Pt films in the second magneticunderlayer 43 was not zero, the write current was gradually increased asthe number of the Co and Pt films was increased. For the case where thenumber of the Co and Pt films was four, the saturation field H_(S) wasincreased up to about 10000 (Oe) and the write current was steeplyincreased to exceed 0.5 mA. According to N. Sakimura et al., “MRAM CellTechnology for Over 500-MHz SoC”, IEEE JOURNAL OF SOLID-STATE CIRCUITS,VOL. 42, NO. 4, pp. 830-838, 2007, the cell area can be reduced to thelevel of existing embedded SRAMs by reducing the write current below 0.5mA.

As thus described, the use of a Co/Pt film stack as the second magneticunderlayer 43 effectively enhanced the perpendicular magnetic anisotropyof the data recording layer 10, when a Co/Ni film stack was used as thedata recording layer 10. In addition, the adjustment of the number ofthe Co and Pt films in the second magnetic underlayer 43 enabledcontrolling the perpendicular magnetic anisotropy of the data recordinglayer 10, sufficiently reducing the write current necessary for causingdomain wall motion (or the domain wall motion current). The range of thesaturation field Hs preferable for adjusting the perpendicular magneticanisotropy to an appropriate value was 3000 (Oe)≦H_(S)≦0.10000 (Oe), andthe number of the Co and Pt films in the second magnetic under layer 43for achieving a saturation field H_(S) in this range was one to three.

As comparative example 1, a magnetoresistance effect element 300 wasfurther prepared as shown in FIG. 10, in which an underlayer 70 wascomposed of a first magnetic underlayer 71 and a non-magnetic underlayer72, where a NiFeB film of a thickness of 2 nm was used as the firstmagnetic underlayer 71, and a Pt film of a thickness of 2 nm was used asthe non-magnetic underlayer 72. Formed on the underlayer 70 was a datarecording layer 10 formed as a Co/Ni film stack in which five Co filmsof a thickness of 0.3 nm and five Ni films of a thickness of 0.6 nm werealternately layered. The magnetoresistance effect element 300 wassubjected to annealing at 350° C. for two hours in vacuum after theunderlayer 70 and the data recording layer 10 were formed, as is thecase with embodiment example 1.

The saturation field Hs of the data recording layer 10 of themagnetoresistance effect element 300 was measured as about 1050 (Oe).Also, it was determined from the magnetization-field loop measured byapplying a magnetic field in the perpendicular direction of the filmsurface that the data recording layer 10 of the magnetoresistance effectelement 300 incorporated in-plane magnetization components and exhibitedvery weak perpendicular magnetic anisotropy. The NiFeB film exhibitsin-plane magnetic anisotropy regardless of the film thickness and themagnetization thereof is increased by thermal annealing. This may bebecause the first magnetic underlayer 71 caused an effect of directingthe magnetization of the data recording layer 10 (Co/Ni film stack) inthe in-plane direction via the non-magnetic underlayer 72, resulting inthat the data recording layer 10 was formed as an in-plane magnetizationfilm which exhibited weak perpendicular magnetic anisotropy.

Furthermore, as embodiment examples 2, magnetoresistance effect elements100 in which a NiFeW film of a thickness of 1.5 nm was used as the firstmagnetic underlayer 41 were additionally prepared. Except for thisaspect, the configuration of the magnetoresistance effect elements 100of embodiment examples 2 was the same as that of embodiment examples 1.In detail, the first magnetic underlayer 41, the non-magnetic underlayer42 and the second magnetic underlayer 43 were serially formed in thisorder as the underlayer 40. A NiFeW film of a thickness of 1.5 nm wasused as the first magnetic underlayer 41, and a Pt film of a thicknessof 2 nm was used as the non-magnetic underlayer 42. A magnetic filmstack in which multiple Co films and multiple Pt films were alternatelylayered was used as the second magnetic underlayer 43. A Co/Ni filmstack in which five Co films of a thickness of 0.3 nm and five Ni filmsof a thickness of 0.6 nm were alternately layered was used as the datarecording layer 10. The magnetoresistance effect elements 100 ofembodiment examples 2 were also subjected to annealing at 350° C. fortwo hours in vacuum. For the magnetoresistance effect elements 100 thusstructured, the change in the magnetization field Hs was examinedagainst the film thickness ratio of the Pt and Co films in the secondmagnetic underlayer 43 and the number of the Pt and Co films. FIG. 11Ais a graph showing the change in the magnetization field H_(S) againstthe number of the Pt and Co films of the second magnetic underlayer 43for different film thickness ratios of the Pt and Co films. As isunderstood from FIG. 11A, for a case where the film thickness ratio ofthe Pt films to the Co films in the second magnetic underlayer 43 was1.0 to 5.0, the saturation field H_(S) ranged from 3000 to 5500 (Oe)when the number of the Co films and Pt films was one to three; thisimplies that the data recording layer 10 exhibited such perpendicularmagnetic anisotropy that current-driven domain wall motion could beachieved.

Furthermore, as examples 3, magnetoresistance effect elements 100 inwhich a NiFeV film of a thickness of 1.5 nm was used as the firstmagnetic underlayer 41 and a Au film of a thickness of 2 nm was wereadditionally prepared. Except for this aspect, the configuration of themagnetoresistance effect elements 100 of examples 3 was the same asthose of embodiment examples 1 and 2. For the magnetoresistance effectelements 100 thus structured, the change in the magnetization fieldH_(S) was examined against the film thickness ratio of the Pt and Cofilms in the second magnetic underlayer 43 and the number of the Pt andCo films. FIG. 11B is a graph showing the change in the magnetizationfield H_(S) against the number of the Pt and Co films of the secondmagnetic underlayer 43 for different film thickness ratios of the Pt andCo films. Also in FIG. 11B, the saturation field H_(S) ranged from 3000to 5500 (Oe) for a case where the film thickness ratio of the Pt filmsto the Co films in the second magnetic underlayer 43 was 1.0 to 5.0;this implies that the data recording layer 10 exhibited suchperpendicular magnetic anisotropy that current-driven domain wall motioncould be achieved.

The above-described results indicate that the preferred film thicknessratio of the Co films and Pt films in the second magnetic underlayer 43is 1.0 to 5.0.

Although the above-described examples are related to the cases where aNiFeZr film or NiFeW film was used as the first magnetic underlayer 41,a Pt film was used as the non-magnetic underlayer 42, and a film stackcomposed of Co and Pt films was used as the second non-magneticunderlayer 43, the materials of the first magnetic underlayer 41, thenon-magnetic underlayer 42 and the second magnetic underlayer 43 are notlimited to those described above. The inventors have confirmed that thesimilar effect can be achieved by using thin film material obtained bydoping base metal of NiFe with at least one non-magnetic materialselected from the group of Ta, Hf and V (in place of Zr and W). Also,the inventors have confirmed that the similar effect can be achieved byusing a Au film, a Pd film or an Ir film as the non-magnetic underlayer42 in place of the Pt film. Furthermore, the inventors have confirmedthat the similar effect can be achieved by using a combination of layersformed of any one of Pt and Pd and layers formed of any one of Fe, Coand Ni as the second magnetic underlayer 43, in place of the combinationof Co films and Pt films.

Second Embodiment

FIG. 12 is a section view showing an exemplary structure of amagnetoresistance effect element 100A of a second embodiment of thepresent invention. The magnetoresistance effect element 100A of thesecond embodiment is structured similarly to the magnetoresistanceeffect element 100 of the first embodiment. The difference exists in thestructure of the underlayer. In the first embodiment, as describedabove, the first magnetic underlayer 41 in the underlayer 40 is formedof material which is intrinsically ferromagnetic with such a thinthickness that the first magnetic underlayer 41 does not exhibitferromagnetism. In the second embodiment, on the other hand, a firstmagnetic underlayer 41A in an underlayer 40A is formed of material whichintrinsically exhibits in-plane magnetic anisotropy, but with such athin thickness (specifically, 0.5 to 3 nm) that the first magneticunderlayer 41A exhibits perpendicular magnetic anisotropy. The firstmagnetic underlayer 41A is formed of amorphous magnetic material whichincludes Co or Fe as the major constituent and at least one non-magneticelement selected from the group consisting of Zr, Ta, W, Hf and V.

The structures of the non-magnetic underlayer 42, the second magneticunderlayer 43 and the data recording layer 10 are the same as those inthe first embodiment. The non-magnetic underlayer 42 is formed of anon-magnetic film which has an fcc structure and exhibits strong (111)orientation. In this embodiment, the non-magnetic underlayer 42 isformed of Pt, Au, Pd or Ir and has a thickness of 0.3 to 4.0 nm. Thesecond magnetic underlayer 43 is formed of a magnetic film stack inwhich at least one first layer and at least one second layer arealternatively layered, where the first layer is formed of any one of Ptand Pd and the second layer is formed of any one of Fe, Co and Ni. Thedata recording layer 10, which is a magnetic film with perpendicularmagnetic anisotropy, is preferably formed of an alternately-layered filmstack of transition metals, such as Co/Ni, Co/Pt, Co/Pd, CoFe/Ni,CoFe/Pt and CoFe/Pd. It is known in the art that the saturationmagnetizations of these materials are relatively small. More generallyspeaking, the data recording layer 10 is structures as a film stack inwhich first and second layers are layered. The first layers include Fe,Co, Ni or alloy of multiple materials selected from the group consistingof Fe, Co and Ni. The second layers include Pt, Pd, Au, Ag, Ni, Cu oralloy of multiple materials selected from the group consisting of Pt,Pd, Au, Ag, Ni and Cu. Among the above-described film stack, the Co/Nifilm stack exhibits high spin polarizability. Therefore, a Co/Ni filmstack is especially preferable as the data recording layer 10.

An advantage of the first magnetic underlayer 41A of the secondembodiment is discussed in the following. As is the case with the firstmagnetic underlayer 41 of the first embodiment, when formed on anamorphous film like the interlayer dielectric 60, the first magneticunderlayer 41A is grown as being amorphous in a thin film thicknessrange of 0.5 to 3.0 nm, enlarging the surface energy thereof. The firstmagnetic underlayer 41A thus structured promotes the closest packedorientation (the orientation with the minimum surface energy face) ofthe crystalline formed thereon. Furthermore, the non-magnetic underlayer42 formed on the first magnetic underlayer 41A is grown so that theclosest packed face thereof is oriented to face the fcc (111) face,since the non-magnetic underlayer 42 is formed of any of Pt, Au, Pd andIr, and a film formed of any of these materials originally has the fccstructure. The data recording layer 10 can be formed with a strongperpendicular magnetic anisotropy by forming a magnetic film over thenon-magnetic underlayer 42, wherein the magnetic film has an fccstructure and exhibits a strong perpendicular magnetic anisotropy forthe (111) orientation. It should be noted that the data recording layer10 can be formed with a strong perpendicular magnetic anisotropy due tothe provision of the first magnetic underlayer 41A, even when thenon-magnetic underlayer 42 has a thin film thickness.

Here, the first magnetic underlayer 41A of the second embodiment isformed of material including Co or Fe as the major constituent and atleast one non-magnetic element selected from the group consisting of Zr,Ta, W, Hf and V, and such material intrinsically exhibits in-planemagnetic anisotropy. One may consider that this undesirably results inthe deterioration of the perpendicular magnetic anisotropy of the datarecording layer. Nevertheless, the first magnetic underlayer 41A of suchmaterial is actually formed as an amorphous magnetic body with weakperpendicular magnetic anisotropy when the thickness of the firstmagnetic underlayer 41A is as thin as 0.5 to 3 nm. As is the case withthe first magnetic underlayer 41 of the first embodiment, which isformed so as to exhibit substantially no magnetization, the firstmagnetic underlayer 41A of the second embodiment does not deterioratethe perpendicular magnetic anisotropy of the data recording layer 10.Therefore, the first magnetic underlayer 41A of the second embodiment isalso preferable for achieving strong perpendicular magnetic anisotropyin the data recording layer 10.

The portions of the first magnetic underlayer 41A positioned on themagnetization fixed layers 50 a and 50 b, on the other hand, effectivelyenhances the magnetic coupling between the data recording layer 10 andthe magnetization fixed layers 50 a and 50 b. For a case where themagnetization fixed layers 50 a and 50 b are formed of hard magneticmaterial, such as a Co/Pt film stack and a Co—Pt alloy film, when thefirst magnetic underlayer 41A and the non-magnetic underlayer 42 aresubsequently layered over the magnetization fixed layers 50 a and 50 b,the magnetizations of the portions of the first magnetic underlayer 41Aon the magnetization fixed layers 50 a and 50 b are directed in theperpendicular directions which are the same directions of that of themagnetization fixed layers 50 a and 50 b, respectively, due to themagnetic interactions from the magnetization fixed layers 50 a and 50 b.Such magnetic interactions fix the magnetizations of portions of thedata recording layer 10 via the non-magnetic underlayer 42, resulting inthat the magnetization fixed regions 11 a and 11 b are formed in thedata recording layer 10. It should be noted that a strong magneticcoupling is achieved between the data recording layer 10 and themagnetization fixed layers 50 a and 50 b, due to the thin film thicknessof the non-magnetic underlayer 42 (0.5 to 4.0 nm).

As will be understood from experimental results described layer, thefirst magnetic underlayer 41A of the second embodiment enhances theperpendicular magnetic anisotropy of the data recording layer 10 moreeffectively than the first magnetic underlayer 41 of the firstembodiment, achieving an increase in the MR ratio of themagnetoresistance effect element. In addition, the first magneticunderlayer 41A of the second embodiment enhances the magnetic couplingbetween the data recording layer 10 and the magnetization fixed layers50 a and 50 b more effectively than the first magnetic underlayer 41 ofthe first embodiment. The experimental results are described in thefollowing.

Experiment 1 Dependence of MR ratio of Magnetic Tunnel Junction onMaterial of Underlayer

Examined first was the dependence of the MR ratio of the magnetic tunneljunction composed of the data recording layer 10, the spacer layer 20and the reference layer 30 on the material of the first magneticunderlayer 41 or 41A. For each magnetoresistance effect element, adielectric film corresponding to the interlayer dielectric 60 was formedon a substrate and the underlayer 40 or 40A, the data recording layer10, the spacer layer 20, and the reference layer 30 were formed. As theunderlayer 40 or 40A, the first magnetic underlayer 41 or 41A, thenon-magnetic underlayer 42 and the second magnetic underlayer 43 wereserially formed in this order.

A NiFeZr film, a CoTa film, a CoZr film or a FeZr film having athickness of 1.5 nm was used as the first magnetic underlayer 41 or 41A.The NiFeW film included 12.5 atomic % tungsten (W) and the remainder wasNiFe base metal. The ratio of Ni to Fe in the NiFe base metal wasNi:Fe=77.5:22.5. The CoTa film included 20 atomic % tantalum (Ta) andthe remainder was Co base metal. The CoZr film included 20 atomic %zirconium (Zr) and the remainder was Co base metal. The FeZr filmincluded 20 atomic % zirconium (Zr) and the remainder was Fe base metal.The NiFeZr film corresponds to the first magnetic underlayer 41 of thefirst embodiment, and The CoTa film, the CoZr film and the FeZr filmcorrespond to the first magnetic underlayer 41A of the secondembodiment.

Furthermore, a Pt film of a thickness of 2 nm was used as thenon-magnetic underlayer 42, and a magnetic film stack in which multipleCo films of a thickness of 0.4 nm and multiple Pt films of a thicknessof 0.8 nm were alternately layered was used as the second magneticunderlayer 43. A Co/Ni film stack in which five Co films of a thicknessof 0.3 nm and five Ni films of a thickness of 0.6 nm were alternatelylayered was used as the data recording layer 10. The samples thusprepared had a width of 100 nm. These samples were subjected toannealing at 300 to 350° C. for two hours in vacuum, after theunderlayer 40 (or 40A), the data recording layer 10, the spacer layer 20and the reference layer 30 were formed.

FIG. 13A is a graph showing the dependency of the MR ratio on thematerial of the first magnetic underlayer (41 or 41A). As shown in FIG.13A, the use of a NiFeZr film (corresponding to the first magneticunderlayer 41 of the first embodiment) resulted in that the magnetictunnel junctions exhibited MR ratios of about 23 to 42 (it should benoted that MR ratios of this range are sufficient for actualimplementations). The use of a CoTa film, a CoZr film or a FeZr film(corresponding to the first magnetic underlayer 41A of the secondembodiment), on the other hand, resulted in that the magnetic tunneljunctions exhibited MR ratios of about 53 to 65, achieving higher MRratios than those achieved by the use of the NiFeZr film. The effect ofimprovement in the MR ratio was especially significant for cases wherethe annealing temperature was low (specifically for an annealingtemperature of 300° C. This result suggests that the first magneticunderlayer 41A of the second embodiment enhances the perpendicularmagnetic anisotropy of the data recording layer 10 more effectively thanthe first magnetic underlayer 41 of the first embodiment, effectivelyincreasing the MR ratio of the magnetoresistance effect element.

Experiment 2 Evaluation of Coupling State between Magnetization FixedLayers 50 a, 50 b and Data Recording Layer 10

Furthermore, the coupling state between the magnetization fixed layers50 a, 50 b and the data recording layer 10 was evaluated. A magneticfilm corresponding to the magnetization fixed layers 50 a and 50 b wereformed on a substrate and the underlayer (40 or 40A) and the datarecording layer 10 were formed on this magnetic film. As the underlayer40 or 40A, the first magnetic underlayer 41 or 41A, the non-magneticunderlayer 42 and the second magnetic underlayer 43 were serially formedin this order.

A NiFeZr film or CoTa film of a thickness of 1.5 nm was used as thefirst magnetic underlayer 41 or 41A. The NiFeZr film corresponds to thefirst magnetic underlayer 41 of the first embodiment, and the CoTa filmcorresponds to the first magnetic underlayer 41A of the secondembodiment. The NiFeZr film included 12.5 atomic % zirconium (Zr) andthe remainder was NiFe base metal. The ratio of Ni to Fe in the NiFebase metal was Ni:Fe=77.5:22.5. The CoTa film included 20 atomic %tantalum (Ta) and the remainder was Co base metal.

Furthermore, a Pt film of a thickness of 2 nm was used as thenon-magnetic underlayer 42, and a magnetic film stack in which multipleCo films of a thickness of 0.4 nm and multiple Pt films of a thicknessof 0.8 nm were alternately layered was used as the second magneticunderlayer 43. A Co/Ni film stack in which five Co films of a thicknessof 0.3 nm and five Ni films of a thickness of 0.6 nm were alternatelylayered was used as the data recording layer 10. The width of thesamples was 100 nm. These samples were subjected to annealing at 300 to350° C. for two hours in vacuum after the underlayer 40 and the datarecording layer 10 were formed.

FIGS. 13B to 13E show the magnetization-field curves of the samples thusobtained. In detail, FIGS. 13B and 13C show the hysteresis loops of thesamples including the first magnetic underlayer 41 based on a NiFeZrfilm, and FIGS. 13D and 13E show the hysteresis loops of the samplesincluding the first magnetic underlayer 41A based on a CoTa film. Whenthere is a sufficiently large magnetic coupling between the magneticfilm corresponding to the magnetization fixed layers 50 a and 50 b andthe Co/Ni film stack corresponding to the data recording layer 10, amagnetization reversal occurs with the magnetic film and the Co/Ni filmstack magnetically coupled as a unit, resulting in that a typicalhysteresis loop with no steps is observed as the magnetization-fieldcurve. When the magnetic coupling is weak, on the other hand,magnetization reversals occur separately in the magnetic film and theCo/Ni film stack, resulting in that a stepwise hysteresis loop isobserved as the magnetization-field curve.

As shown in FIGS. 13B and 13C, the first magnetic underlayer 41 based onthe NiFeZr film achieved a hysteresis loop with no steps for anannealing temperature of 350° C.; however, a stepwise hysteresis loopwas observed for an annealing temperature of 300° C. This suggests thatthe use of a NiFeZr film as the first magnetic underlayer 41 with anannealing temperature of 300° C. undesirably weakened the magneticcoupling between the magnetic film corresponding to the magnetizationfixed layers 50 a and 50 b and the Co/Ni film stack corresponding to thedata recording layer 10.

As shown in FIGS. 13D and 13E, on the other hand, the first magneticunderlayer 41A based on the CoTa film achieved a hysteresis loop with nosteps for both of the annealing temperatures of 300 and 350° C. Thissuggests that the use of a CoTa film as the first magnetic underlayer41A achieves sufficiently strong magnetic coupling between the magneticfilm corresponding to the magnetization fixed layers 50 a and 50 b andthe Co/Ni film stack corresponding to the data recording layer 10.

Experiment 3 Magnetic Property of First Magnetic Underlayer 41A

Next, a description is given of the magnetic property and the preferredfilm thickness range of the first magnetic underlayer 41A. In order tostudy a portion of the first magnetic underlayer 41A in contact with theinterlayer dielectric 60 (formed of a SiN or SiO₂ film), CoTa films wereformed on substrates in which a SiN film of 20 nm was deposited on a Sisubstrate, and the magnetizations of the CoTa films were measured. Thethicknesses of the formed CoTa films ranged from 0.5 to 5 nm. The formedCoTa films include 20 atomic % tantalum (Ta) and the remainder was Cobase metal. The samples were subjected to annealing at 350° C. for twohours in vacuum.

FIG. 14A shows the magnetization-field curves of the CoTa films when themagnetic field was applied in the perpendicular direction of the filmsurface in the magnetization measurements, and FIG. 14B shows the changein the magnitude of the magnetization against the thickness of the CoTafilm. Such measurements are equivalent to measurements of theperpendicular magnetic anisotropies of the samples. As shown in FIG.14A, the CoTa film did not exhibit magnetization for a thickness of 0.5nm. Such CoTa film (which does not exhibit in-plane magnetic anisotropy)is suitable as the first magnetic underlayer 41A, causing no magneticinfluence on occurrence of the perpendicular magnetic anisotropy of thedata recording layer 10.

In a film thickness range from 1.0 to 3.0 nm, hysteresis loops wereobtained as the magnetization-field curves. It should be noted that themagnetizations of the CoTa films in the perpendicular direction of thefilm surfaces were small in the film thickness range from 1.0 to 3.0 nmas shown in FIG. 14B. The magnetization in the perpendicular directionof the film surface showed a small increase against the increase in thefilm thickness. This implies that the CoTa film exhibits smallperpendicular magnetic anisotropy in the film thickness range of 1.0 to3 nm. Such CoTa film (which does not exhibit in-plane magneticanisotropy) is suitable as the first magnetic underlayer 41A, causing nomagnetic influence on occurrence of the perpendicular magneticanisotropy of the data recording layer 10.

It should be noted that the first magnetic underlayer 41A does notprovide its originally-intended function of enhancing crystal growth ina film thickness range below 0.5 nm. Therefore, when a CoTa film is usedas the first magnetic underlayer 41A, the thickness of the CoTa film isdesirably in the range from 0.5 nm to 3.0 nm.

When the film thickness was 4.0 nm, on the other hand, the magnetizationin the perpendicular direction of the film surface was reduced as shownin FIG. 14A. This resulted from that a large magnetization was generatedin the CoTa film in the in-plane direction, that is, a large in-planemagnetic anisotropy was generated. Since a large in-plane magneticanisotropy is generated in the CoTa film for film thicknesses of 4.0 nmor more, such CoTa film is not suitable as the first magnetic underlayer41A.

The above-described results indicate that the preferred film thicknessrange of the CoTa film as the first magnetic underlayer 41A is from 0.5nm to 3.0 nm.

The inventors have confirmed that the same applies to the CoZr film, theFeTa film and the FeZr film as well as the CoTa film described above.

Experiment 4 Effect of Structure of Second Magnetic Underlayer 43

Furthermore, the effect of the number of layers of the second magneticunderlayer 43 in the magnetoresistance effect element was examined wherethe above-described first magnetic underlayer 41A of the secondembodiment is applied. Specifically, samples of the following structureswere prepared: A first magnetic underlayer 41, a non-magnetic underlayer42 and a second magnetic underlayer 43 were sequentially layered in thisorder as the underlayer 40A of each magnetoresistance effect element. ACoTa film of a thickness of 1.5 nm was used as the first magneticunderlayer 41A, and a Pt film of a thickness of 2 nm was used as thenon-magnetic underlayer 42. The CoTa film included 20 atomic % tantalum(Ta) and the remainder was Co base metal. A magnetic film stack in whichone or more Co films of a thickness of 0.4 nm and one or more Pt filmsof a thickness of 0.8 nm were alternately layered was used as the secondmagnetic underlayer 43. A Co/Ni film stack in which five Co films of athickness of 0.3 nm and five Ni films of a thickness of 0.6 nm werealternately layered was used as the data recording layer 10. Themagnetoresistance effect elements 100 of the above-described structurewere prepared, wherein the number of the Co and Pt films in the secondmagnetic underlayer 43 was varied from zero to four. The width of thesamples was 100 nm. These samples were subjected to annealing at 350° C.for two hours in vacuum, after the underlayer 40A and the data recordinglayer 10 were formed.

FIGS. 15A to 15C are diagrams showing the magnetization-field curves ofthe data recording layers 10 for cases where the number of the Co and Ptfilms within the second magnetic underlayer 43 was zero to two. For thecase where the number of the Co and Pt films was zero (that is, the casewhere the second magnetic underlayer 43 was not provided), as shown inFIG. 15A, the data recording layer 10 exhibited relatively weakperpendicular magnetic anisotropy, incorporating an in-planemagnetization component. As shown in FIGS. 15B and 15C, on the otherhand, there was a tendency in which the M-H loops became morerectangular and the perpendicular magnetic anisotropy was enhanced asthe number of the layered Co and Pt films was increased. This impliesthat the use of the second magnetic underlayer 43 enables achievingstrong perpendicular magnetic anisotropy for the case where a Co/Ni filmstack, for which it is relatively difficult to achieve the fcc (111)orientation, is used as the data recording layer 10, even after theannealing at 350° C. for two hours.

This fact has two technical meanings: First, the use of a Co/Pt magneticfilm stack as the data recording layer 10 effectively achieves strongperpendicular anisotropy for the data recording layer 10. Second, theuse of a Co/Pt magnetic film stack as the second magnetic underlayer 43enables forming the second magnetic underlayer 43 with improved fcc(111) orientation, effectively improving the perpendicular magneticanisotropy of the data recording layer 10 formed thereon (for example,formed of a Co/Ni magnetic film stack).

Furthermore, the saturation field H_(S) was measured for a case where aCoTa film was used as the first magnetic underlayer 41A, a Co/Ptmagnetic film stack was used as the second magnetic underlayer 43 and aCo/Ni magnetic film stack was used as the data recording layer 10. FIG.16 shows the change in the saturation field H_(S) of the data recordinglayer 10 against the number of the Co and Pt films in the secondmagnetic underlayer 43, where the number of the Co and Pt films wasvaried from zero to four. As is understood from FIG. 16, the saturationfield H_(S) was increased as the number of the Co and Pt films in thesecond magnetic underlayer 43; this implies that the perpendicularmagnetic anisotropy was enhanced as the number of the Co and Pt filmswas increased.

FIG. 17 shows the changes in the saturation field H_(S) and the writecurrent against the number of the Co and Pt films in the second magneticunderlayer 43. The magnitude of the write current is defined as theminimum write current necessary for causing domain wall motion in thedata recording layer 10. Details of the experimental procedure are alsodescribed in T. Suzuki et al., “Evaluation of Scalability forCurrent-Driven Domain Wall Motion in a Co/Ni Multilayer Strip for MemoryApplications”, IEEE TRANSACTIONS ON MAGNETICS, VOL. 45, NO. 10, pp.3776-3779, (2009), the disclosure of which is incorporated herein byreference.

For samples in which the number of the Co and Pt films in the secondmagnetic underlayer 43 was zero (this implies that the second magneticunderlayer 43 was not deposited), domain wall motion by the current wasnot observed clearly, resulting in an unsuccessful measurement of thewrite current. This can be considered as resulting from that the datarecording layer 10 exhibited relatively weak perpendicular magneticanisotropy and incorporated in-plane magnetization components as shownin FIG. 15A.

For cases where the number of the Co and Pt films in the second magneticunderlayer 43 was not zero, the write current was gradually increased asthe number of the Co and Pt films was increased. For the case where thenumber of the Co and Pt films was four, the saturation field H_(S) wasincreased up to about 10000 (Oe) and the write current was steeplyincreased to exceed 0.5 mA. According to N. Sakimura et al., “MRAM CellTechnology for Over 500-MHz SoC”, IEEE JOURNAL OF SOLID-STATE CIRCUITS,VOL. 42, NO. 4, pp. 830-838, 2007, the cell area can be reduced to thelevel of existing embedded SRAMs by reducing the write current below 0.5mA.

As thus described, the use of a Co/Pt film stack as the second magneticunderlayer 43 effectively enhanced the perpendicular magnetic anisotropyof the data recording layer 10, when a CoTa film was used as the firstmagnetic underlayer 41A and a Co/Ni film stack was used as the datarecording layer 10. In addition, the adjustment of the number of the Coand Pt films in the second magnetic underlayer 43 enabled controllingthe perpendicular magnetic anisotropy of the data recording layer 10,sufficiently reducing the write current necessary for causing domainwall motion (or the domain wall motion current). The range of thesaturation field H_(S) preferable for adjusting the perpendicularmagnetic anisotropy to an appropriate value was 3000 (Oe)≦H_(S)≦0.10000(Oe), and the number of the Co and Pt films in the second magnetic underlayer 43 for achieving a saturation field H_(S) in this range was one tothree.

Furthermore, the effect of the film thickness ratio of the Pt and Cofilms in the second magnetic underlayer 43 was examined. In detail, thefirst magnetic underlayer 41A, the non-magnetic underlayer 42 and thesecond magnetic underlayer 43 were serially formed in this order as theunderlayer 40A. A CoTa film of a thickness of 1.5 nm was used as thefirst magnetic underlayer 41A, and a Pt film of a thickness of 2 nm wasused as the non-magnetic underlayer 42. A magnetic film stack in whichmultiple Co films and multiple Pt films were alternately layered wasused as the second magnetic underlayer 43. A Co/Ni film stack in whichfive Co films of a thickness of 0.3 nm and five Ni films of a thicknessof 0.6 nm were alternately layered was used as the data recording layer10. The samples were subjected to annealing at 350° C. for two hours invacuum. For the samples thus structured, the change in the magnetizationfield H_(S) was examined against the film thickness ratio of the Pt andCo films in the second magnetic underlayer 43 and the number of the Ptand Co films.

FIG. 18 is a graph showing the change in the magnetization field H_(S)against the number of the Pt and Co films of the second magneticunderlayer 43 for different film thickness ratios of the Pt and Cofilms. As is understood from FIG. 18, for a case where the filmthickness ratio of the Pt films to the Co films in the second magneticunderlayer 43 was 1.0 to 5.0, the saturation field H_(S) ranged from3000 to 5500 (Oe) when the number of the Co films and Pt films was oneto three; this implies that the data recording layer 10 exhibited suchperpendicular magnetic anisotropy that current-driven domain wall motioncould be achieved.

Third Embodiment

FIG. 19A is a section view showing an exemplary configuration of amagnetoresistance effect element 100B of a third embodiment of thepresent invention, and FIG. 19B is a section view showing an exemplaryconfiguration of a magnetic recording layer of the magnetoresistanceeffect element 100B of the third embodiment. It should be noted thatFIG. 19B is the section view on the SS' section in FIG. 19A.

The magnetoresistance effect element 100B of the third embodiment isstructured similarly to the magnetoresistance effect element 100 of thefirst embodiment. The difference exists in the structure of theunderlayer. In the first embodiment, the underlayer 40 incorporates thefirst magnetic underlayer 41, the non-magnetic underlayer 42 and thesecond magnetic underlayer 43. In the third embodiment, on the otherhand, the underlayer 40B fails to include a component corresponding tothe second magnetic underlayer 43 of the first embodiment, whileincorporating the magnetic underlayer 41 and an intermediate layer 42B(which corresponds to a non-magnetic underlayer). The data recordinglayer 10 is formed on the intermediate layer 42B. In the firstembodiment, it has been already discussed that the second magneticunderlayer 43 is not an essential component; in this embodiment, apreferred structure will be presented for a case where the secondmagnetic underlayer 43 is not provided.

The magnetization fixed layers 50 a and 50 b are embedded in groovesformed on the interlayer dielectric 60. Embedded under the interlayerdielectric 60 (such as, SiO₂ and SiN_(x)) are elements (such as,selection transistors Tra and Trb) and interconnections (such as, wordlines WL and bit lines BL and /BL).

The magnetic underlayer 41 is formed on the upper faces of theinterlayer dielectric 60 and the magnetization fixed layers 50 a and 50b. The magnetic underlayer 41 is in contact with the upper faces of themagnetization fixed layers 50 a and 50 b on the bottom face (−z side) atthe end portions (in the x directions). The magnetic underlayer 41 isformed of magnetic material. As discussed above, the ferromagnetism ofthe magnetic underlayer 41 enhances the magnetic coupling between themagnetization fixed layers 50 a, 50 b and the data recording layer 10.

It is preferable that the magnetic underlayer 41 is amorphous or has amicrocrystalline structure, since this improves the surface flatness ofthe magnetic underlayer 41. The microcrystalline structure of themagnetic underlayer 41 may be in a crystalline phase formed of crystalswith grain sizes of several to 20 nm, for example. Alternatively, themagnetic underlayer 41A may be formed as a mixture of a crystallinephase and amorphous phase. The smooth surface of the magnetic underlayer41 is preferable for forming the data recording layer 10, which isdeposited above the magnetic underlayer 41 across the intermediate layer42B, so that the data recording layer 10 has desired crystallinity. Whenthe data recording layer 10 is a [Co/Ni]_(n)/Pt film, for example, thesmooth surface of the magnetic underlayer 41 is preferable for allowingthe [Co/Ni] film stack to exhibit fcc (111) orientation, which causeshigh perpendicular magnetic anisotropy.

The magnetic underlayer 41 includes at least one of Ni, Fe and Co as themajor constituent and at least one non-magnetic element selected fromthe group consisting of Zr, Hf, Ti, V, Nb, Ta, W, B and N. Please notethe “major constitute” means the constituent which exists most in themagnetic underlayer 41. The magnetic underlayer 41 may be formed of, forexample, NiFeZr, CoFeB, CoZrMo, CoZrNb, CoZr, CoZrTa, CoHf, CoTa,CoTaHf, CoNbHf, CoZrNb, CoHfPd, CoTaZrNb, CoZrMoNi or CoTi.

The intermediate layer 42B is a non-magnetic body formed to cover themagnetic underlayer 41. In order to enhance the perpendicular magneticanisotropy of the data recording layer 10, which is formed on theintermediate layer 42B, the intermediate layer 42B is preferably formedof material with a small surface energy to improve the crystallineorientation. In one example, the intermediate layer 42B is formed of aTa film. When the intermediate layer 42B is formed of a Ta film, theintermediate layer 42B preferably has a thickness of 0.1 to 2.0 nm, asdescribed below. When the thickness of the intermediate layer 42B isless than 0.1 nm, the effect of the enhancement of the perpendicularmagnetic anisotropy of the data recording layer 10 is significantlydeteriorated. When the thickness of the intermediate layer 42B is morethan 2.0 nm, the magnetic coupling is lost between the magnetizationfixed layers 50 a, 50 b and the data recording layer 10.

The data recording layer 10 is a ferromagnetic body with perpendicularmagnetic anisotropy which is formed to cover the intermediate layer 42B.The magnetization fixed regions 11 a, 11 b and the magnetization freeregion 13 are formed within the data recording layer 10. In other words,the data recording layer 10 is a region in which a domain wall is formedand data are stored as the magnetization direction of the magnetizationfree region 13 or as the position of the domain wall. The recordinglayer 10 may be formed of ferromagnetic material with perpendicularmagnetic anisotropy, such as those described in the first and secondembodiments.

In the following, an example of the magnetoresistance effect element ofthe third embodiment is described with comparison with comparativeexamples. The saturation field is used as the index of the magnitude ofthe perpendicular magnetic anisotropy. The definition of the saturationfield is as defined above with reference to FIG. 7.

Comparative Example 1

FIGS. 20A and 20B are section views showing the configuration of amagnetoresistance effect element 300B of comparative example 1. Itshould be noted that the spacer layer 20 and the reference layer 30 arenot shown. A SiO₂ film was used as the interlayer dielectric 60 in oneexample. A [Co/Ni]_(n)/Pt film stack in which a Pt film 10 b and a Co/Nifilm stack 10 a were layered was used as the data recording layer 10,where the Co/Ni film stack 10 a was formed of Co films and Ni filmswhich were alternatively layered; the [Co/Ni]_(n)/Pt film stack exhibitsperpendicular magnetic anisotropy and is suitable for domain wallmotion. A Pt film 10 c was additionally deposited as a cap layer.

The [Co/Ni]_(n)/Pt film stack exhibits high perpendicular magneticanisotropy when the Co/Ni film stack incorporated therein has fcc (111)orientation. The crystalline orientation of the Co/Ni film stack,however, depends on the material and structure of the underlayer, andthe magnitude of the perpendicular magnetic anisotropy also depends onthe material and structure of the underlayer. In comparative example 1,the data recording layer 10 was deposited directly on the magneticunderlayer 41 without using the intermediate layer 42B. A NiFeZr film ofa thickness of 2.0 nm was used as the magnetic underlayer 41. In thisexperiment, the samples were not patterned to evaluate the intrinsicmagnetic properties. That is, the magnetic properties of the datarecording layer 10 were evaluated in the as-deposited state (in thestate of an as-deposited Pt/[Co/Ni]_(n)/Pt/NiFeZr film stack). Avibrating sample magnetometer (VSM) was used for the evaluation of themagnetic properties (the same goes for the following).

First, a description is given of the magnetic property of the datarecording layer 10 before subjected to an annealing process after thedeposition. FIGS. 21A and 21B are graphs showing exemplary magnetizationcurves in a case where external magnetic fields were applied to the datarecording layer 10 of the structure shown in FIGS. 20A and 20B. Thevertical axis represents the product of the magnetization M and the filmthickness t (arbitrary unit) and the horizontal axis represents theapplied external field H (Oe). It should be noted that FIG. 21A showsthe magnetization curve in a case where the external magnetic field Hwas applied in the perpendicular direction of the film surface, and FIG.21B shows the magnetization curve in a case where the external magneticfield H was applied in the in-plane direction of the film surface. Themagnetization curve for the perpendicular magnetic field (theperpendicular loop shown in FIG. 21A) showed a steep shape and a largehysteresis, while the magnetization curve for the in-plane magneticfield (the in-plane loop shown in FIG. 21B) showed a slanting shape.This implies that the data recording layer 10 exhibited perpendicularmagnetic anisotropy. In other words, the [Co/Ni]_(n)/Pt film stack onthe NiFeZr film exhibited perpendicular magnetic anisotropy, and therewas a possibility in which the [Co/Ni]_(n)/Pt film stack might besuitable for domain wall motion.

Next, a description is given of the magnetic property of the datarecording layer 10 after subjected to a thermal annealing in inert gasat 300° C. for two hours. FIGS. 22A and 22B are graphs showing exemplarymagnetization curves in a case where external magnetic fields wereapplied to the data recording layer 10 of the structure shown in FIGS.20A and 20B after the data recording layer 10 was subjected to thethermal annealing. The vertical axis represents the product of themagnetization M and the film thickness t (arbitrary unit) and thehorizontal axis represents the applied external field H (Oe). It shouldbe noted that FIG. 22A shows the magnetization curve in a case where theexternal magnetic field H was applied in the perpendicular direction ofthe film surface, and FIG. 22B shows the magnetization curve in a casewhere the external magnetic field H was applied in the in-planedirection of the film surface. Compared to FIGS. 21A and 21B, theperpendicular loop was deformed into a more slanting shape as shown inFIG. 22A, while the in-plane loop was modified into a more steep shapeas shown in FIG. 22B. This implies that the perpendicular magneticanisotropy of the data recording layer 10 was deteriorated by thethermal annealing at 300° C. Furthermore, as is understood from thecomparison between FIGS. 21A and 22A, the product of the saturationmagnetization and the thickness (M_(s)×t) was increased after thethermal annealing, as shown in FIG. 22A. This results from that theNiFeZr film, which intrinsically has in-plane magnetic anisotropy, wasmagnetically coupled to the [Co/Ni]_(n)/Pt film stack by the thermalannealing at 300° C., causing an increase in the magnetization. Themagnetic coupling between the NiFeZr film and the [Co/Ni]_(n)/Pt filmstack deteriorates the perpendicular magnetic anisotropy of the[Co/Ni]_(n)/Pt film stack.

Comparative Example 2

In comparative example 2, the structure of the data recording layer 10was the same as that in comparative example 1 (in which a NiFeZr filmwas used as the magnetic underlayer 41), except for that a Ta film wasused in place of the magnetic underlayer 41. When the Ta film is used,the thickness of the Ta film was required to be 4.0 nm or more, in orderto achieve fcc (111) orientation of the Co/Ni film stack. This thicknessis very large, twice as large as the film thickness of the NiFeZr film(2.0 nm) in comparative example 1. Due to the large thickness of the Tafilm, which is non-magnetic material, it was difficult to achievemagnetic coupling between the magnetization fixed layers 50 a, 50 b andthe data recording layer 10 in comparative example 2. This potentiallyresults in that the magnetizations of the magnetization fixed regions 11a and 11 b are not fixed and data cannot be stored in the data recordinglayer 10.

From comparative examples 1 and 2, the inventors created the followingembodiment example, considering avoiding unnecessary magnetic couplingbetween the NiFeZr film and the [Co/Ni]_(n)/Pt film stack after thethermal annealing and avoiding disconnection of the magnetic couplingbetween the magnetization fixed layers 50 a, 50 b and the data recordinglayer 10.

Embodiment Example 1

FIGS. 23A and 23B shows section views showing an exemplary structure ofa magnetoresistance effect element of embodiment example 1. It should benoted that the spacer 20 and the reference layer 30 are not shown. ASiO₂ film was used as the interlayer dielectric 60 in one example. As isthe case with comparative example 1, a [Co/Ni]_(n)/Pt film stack inwhich a Pt film 10 b and a Co/Ni film stack 10 a were layered was usedas the data recording layer 10, where the Co/Ni film stack 10 a wasformed of Co films and Ni films which were alternatively layered; the[Co/Ni]_(n)/Pt film stack exhibits perpendicular magnetic anisotropy andis suitable for domain wall motion. A Pt film 10 c was also additionallydeposited as a cap layer.

Embodiment example 1 was modified from comparative example 1, so thatthe intermediate layer 42B was inserted between the magnetic underlayer41 (the NiFeZr film) and the data recording layer 10 (the [Co/Ni]_(n)/Ptfilm stack) so that they were not magnetically coupled. A Ta film of athickness of 2.0 nm was used as the intermediate layer 42B. The sampleswere subjected to a thermal annealing at 300° C. for two hours in inertgas, after being formed into a Pt/[Co/Ni]_(n)/Pt/Ta/NiFeZr film stack.

Next, a description is given of the magnetic property of the datarecording layer 10 after subjected to a thermal annealing in inert gasat 300° C. for two hours.

FIGS. 24A and 24B are graphs showing exemplary magnetization curves in acase where external magnetic fields were applied to the data recordinglayer 10 of the structure shown in FIGS. 23A and 23B. The vertical axisrepresents the product of the magnetization M and the film thickness t(arbitrary unit) and the horizontal axis represents the applied externalfield H (Oe). It should be noted that FIG. 24A shows the magnetizationcurve in a case where the external magnetic field H was applied in theperpendicular direction of the film surface, and FIG. 24B shows themagnetization curve in a case where the external magnetic field H wasapplied in the in-plane direction of the film surface. As is understoodfrom the comparison to FIGS. 21A, 21B, 22A and 22B, the data recordinglayer 10 of embodiment example 1 showed a more slanting in-plane loopand this means that a larger perpendicular magnetic anisotropy wasachieved even after the thermal annealing at 350° C. Furthermore, as isunderstood from the comparison to FIG. 22B, the saturation field H_(S)(See FIG. 7) was increased in embodiment example 1, as shown in FIG.24B. In other words, the data recording layer 10 of embodiment example 1showed a larger external magnetic field necessary for directing themagnetization in the direction of the external magnetic field as shownin FIG. 24B. As thus described, the data recording layer 10 for whichthe Ta film was inserted as the intermediate layer 42B as shown in FIGS.23A and 23B exhibited larger perpendicular magnetic anisotropy than thedata recording layer 10 shown in FIGS. 20A and 20B, from which theintermediate layer 42B was excluded.

In the following, a description is given of the change in the saturationfield H_(S) against the thickness of the intermediate layer 42B and thetemperature of the thermal annealing. FIG. 25 is a graph showing oneexample of the change in the saturation field H_(S) against thethickness of the intermediate layer 42B and the temperature of thethermal annealing. The vertical axis represents the saturation fieldH_(S) (Oe) and the horizontal axis represents the thickness of the Tafilm used as the intermediate layer 42B. The circular dots indicate thesaturation field H_(S) obtained after the thermal annealing at 200° C.,and the triangular marks indicate the saturation field H_(S) obtainedafter the thermal annealing at 350° C. For both of the thermal annealingprocesses at 200° C. and 350° C., the data recording layer 10 for whichthe Ta film was provided with a thickness of 0.1 nm or more showedhigher saturation fields H_(S) and exhibited larger perpendicularmagnetic anisotropy, compared to the data recording layer 10 for whichthe Ta film was not provided. The saturation field H_(S) was saturatedfor the configuration in which the thickness of the Ta film was 2.0 nmor more.

This implies that it is unnecessary to increase the thickness of the Tafilm more than 2.0 nm. Rather, the magnetization fixed layers 50 a and50 b cannot be magnetically coupled to the data recording layer 10 ifthe thickness of the Ta film, which is non-magnetic, is excessivelyincreased. This potentially results in that the magnetizations of themagnetization fixed regions 11 a and 11 b are not fixed and data cannotbe stored in the data recording layer 10. In addition, the increases inthe thicknesses of the magnetic underlayer 41 and the intermediate layer42B increase the section area of the route of the write current,including the data recording layer 10, and this may cause difficulty inthe control of the write current due to the manufacture variations.Therefore, the Ta film preferably has a thickness of 0.1 to 2.0 nm, morepreferably, 0.2 nm to 1.0 nm.

As is understood from the above-described results, the insertion of theintermediate layer 42B (for example, a Ta film) allowed the datarecording layer 10 shown in FIGS. 23A and 23B to exhibit higherperpendicular magnetic anisotropy even after the high temperaturethermal annealing at 350° C., compared to the data recording layer 10for which the intermediate layer 42B was not inserted (that is, thethickness of the Ta film is zero). This can be considered as resultingfrom that the magnetic coupling between the NiFeZr film (the magneticunderlayer 41), which has in-plane magnetic anisotropy, and the[Co/Ni]_(n)/Pt film stack (the data recording layer 10) was suppressedby the Ta film (the intermediate layer 42B).

In addition, it was confirmed that the magnetic coupling was maintainedbetween the magnetization fixed layers 50 a, 50 b and the data recordinglayer 10, even for the case where the sum of the thicknesses of theintermediate layer 42B and the magnetic underlayer 41 was as large as4.0 nm. In other words, the magnetizations of the magnetization fixedregions 11 a and 11 b were fixed by the magnetization fixed layers 50 aand 50 b. This may be because the increase in the total thickness up to4.0 nm was the result of the increases in the thicknesses of both of thenon-magnetic Ta film and the magnetic NiFeZr film, not the result of theincrease in the thickness of only the non-magnetic Ta film. The magneticNiFeZr film possibly provides some contribution to the magnetic couplingbetween the magnetic fixed layers 50 a, 50 b and the data recordinglayer 10.

As thus described, the insertion of a Ta film of a thickness of 0.1 to2.0 nm as the intermediate layer 42B between the magnetic underlayer 41and the data recording layer 10 effectively improves the perpendicularmagnetic anisotropy and the suitability to domain wall motion of thedata recording layer 10. The insertion of the Ta film also providesthermal resistance for the data recording layer 10, avoiding anundesired influence on the magnetic coupling between the magnetizationfixed layers and the magnetization fixed regions of the data recordinglayer 10. As a result, a magnetic memory can be obtained in which thedata recording layer exhibits strong perpendicular magnetic anisotropyafter the completion of the manufacture process of the magnetic memory.

Embodiment Example 2

The structure of the data recording layer 10 of embodiment example 2 wassimilar to that of embodiment example 1; the difference of embodimentexample 2 from embodiment example 1, in which the intermediate layer 42Bis formed of a Ta film, is that a Ru film or a Mg film was used as theintermediate layer 42B. FIG. 26 is a graph showing an example of themagnetization curve in a case where an external field was applied to adata recording layer structured as shown in FIGS. 23A and 23B. Thevertical axis represents the produce of the magnetization M and the filmthickness t (arbitrary unit) and the horizontal axis represents theapplied magnetic field (Oe). It should be noted that FIG. 26 shows thein-plane loop, which is the magnetization curve in a case where theexternal field H was applied in the in-plane direction. In FIG. 26, themagnetization curve E indicates the case where the Ta film is used asthe intermediate layer 42B (embodiment example 1). The magnetizationcurve F indicates the case where the Ru film is used as the intermediatelayer 42B, and the magnetization curve G indicates the case where the Mgfilm is used. The thickness of the Ru film, the Mg film and the Ta filmwas 1.0 nm and the samples were not subjected to thermal annealing.

As shown in FIG. 26, the in-plane loop for the Ta film (themagnetization loop E) showed the smallest slant angle and a highsaturation field H_(S). The difference in the magnetic properties of theRu film and the Mg film from the Ta film can be considered as resultingfrom the difference in the fcc (111) orientation of the [Co/Ni]_(n)/Ptfilm stack. The above-described results showed that a Ta film wasconsiderably suitable as the intermediate layer 42B for enhancing fcc(111) orientation, which is strongly related to perpendicular magneticanisotropy of the [Co/Ni]_(n)/Pt film stack. The results also showedthat a Ru film and a Mg film were not necessarily suitable as theintermediate layer 42B, at least when they were individually used. A Rufilm or a Mg film may be usable in a form of a film stack including a Tafilm.

Configurations of Magnetic Memory and Memory Cells

The magnetoresistance elements 100, 100A and 100B of the above-describedembodiments may be used as memory cells in a magnetic memory. In thefollowing, a description is given of exemplary structures of a magneticmemory and memory cells incorporated therein, in one embodiment.

FIG. 27 is a block diagram showing an exemplary configuration of amagnetic memory 90 in one embodiment of the present invention. Themagnetic memory 90 includes a memory cell array, an X driver 92, a Ydriver 93 and a controller 94. The memory cell array 91 includes aplurality of memory cells 80 arranged in an array, a plurality of wordlines WL, a plurality of pairs of bit lines BLa, BLb, a plurality ofground lines GL. Each memory cell 80 is connected to the correspondingword line WL, the corresponding ground line GL and the correspondingpair of bit lines BLa and BLb. The X driver 92 drives the word lineconnected to the memory cell 80 to be accessed, which is selected fromthe plurality of word lines WL. The Y driver 93 is connected to thepairs of the bit lines BLa and BLb, and drives each bit line to adesired state depending on the write operation and the read operation.The controller 94 controls the X driver 92 and the Y driver 93 dependingon the write operation and the read operation.

FIG. 28 is a schematic circuit diagram showing an exemplaryconfiguration of the memory cells 80 in one embodiment of the presentinvention. Each memory cell, which is structured as a 2T-1MTJ (twotransistors−one magnetic tunnel junction) structure, includes amagnetoresistance effect element described above (100, 100A or 100B),and a pair of transistors TRa and TRb. The magnetoresistance effectelement (100, 100A or 100B) includes three terminals. The terminalconnected to the reference layer 30 of the magnetoresistance effectelement (100, 100A or 100B) is connected to the corresponding groundline GL. The terminal connected to the magnetization fixed regions 11 aof the data recording layer 10 is connected to the corresponding bitline BLa via the transistor TRa, and the terminal connected to themagnetization fixed regions 11 b of the data recording layer 10 isconnected to the corresponding bit line BLa via the transistor TRa. Thegates of the transistor TRa and TRb are commonly connected to the wordline WL.

The access to the memory cell 80 is achieved as follows: In the writeoperation, the word line WL is set to the high level to turn on thetransistors TRa and TRb. In addition, one of the bit lines BLa and BLbis set to the high level and the other is set to the low level (theground level). As a result, a write current is flown between the bitlines BLa and BLb via the transistors TRa, TRb and the data recordinglayer 10. This achieves writing desired data into the data recordinglayer 10.

In the read operation, on the other hand, the word line WL is set to thehigh level to turn on the transistors TRa and TRb. The bit line BLa isplaced into the high impedance state and the bit line BLb is set to thehigh level. As a result, a read current Iread is flown from the bit lineBLb to the ground line GL via the MTJ of the magnetoresistance effectelement (100, 100A or 100B). The data stored in the data recording layer10 of the magnetoresistance effect element are identified by detectingthe read current Iread.

Although embodiments and embodiment examples of the present inventionare specifically described above, the present invention should not beinterpreted as being limited to the above-described embodiments andembodiment examples. It should be noted that the present invention maybe implemented with various changes and modifications apparent to theperson skilled in the art.

What is claimed is:
 1. A magnetic memory, comprising: a ferromagneticunderlayer comprising a magnetic material; a non-magnetic intermediatelayer disposed on said underlayer; a ferromagnetic data recording layerformed on said intermediate layer and having a perpendicular magneticanisotropy; a reference layer connected to said data recording layeracross a non-magnetic layer; and first and second magnetization fixedlayers disposed in contact with a bottom face of said underlayer,wherein said data recording layer includes: a magnetization free regionhaving a reversible magnetization and opposed to said reference layer; afirst magnetization fixed region coupled to a first border of saidmagnetization free layer and having a magnetization fixed in a firstdirection; and a second magnetization fixed region coupled to a secondborder of said magnetization free layer and having a magnetization fixedin a second direction opposite to said first direction, and wherein saidintermediate layer comprises a Ta film having a thickness of 0.1 to 2.0nm.
 2. The magnetic memory according to claim 1, wherein said underlayeris amorphous or includes a microcrystalline structure.
 3. The magneticmemory according to claim 1, wherein said underlayer includes at leastone of Ni, Fe, and Co as a major constitution, and further includes atleast one non-magnetic element selected from the group consisting of Zr,Hf, Ti, V, Nb, Ta, W, B, and N.
 4. The magnetic memory according toclaim 1, wherein said data recording layer comprises n film stacks ineach of which first and second layers are layered, where n is a naturalnumber, wherein said first layer includes at least one material selectedfrom the group consisting of Fe, Co, and Ni, and wherein said secondlayer comprises a material different from that of said first layer andincludes at least one material selected from the group consisting of Fe,Co, and Ni.